I'm not saying you have schizophrenia but it's another example that a disease besides bipolar disorder can cause mood instability. My psychiatrist diagnosed me with it and he asks me all the time how my mood has been and before I took an antipsychotic my emotions constantly changed by the second to just about anything you can think of.
The symptoms you are describing sound like you may have borderline personality disorder, the DSM criteria are below. However, your moods seem to be impacting your close relationships, so whether or not you have a defined mental illness, it may be helpful for you to talk to a mental health professional.
borderline personality disorder
A pervasive pattern of instability of interpersonal relationships, self-image, and affects, and marked impulsivity beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:
1) frantic efforts to avoid real or imagined abandonment
2) a pattern of unstable & intense interpersonal relationships characterized by alternating between extremes of idealization and devaluation
3) identity disturbance: markedly and persistent unstable self-image or sense of self
4) impulsivity in at least two areas that are potentially self-damaging (e.g. spending, sex, substance abuse, reckless driving, binge eating)
5) recurrent suicidal behavior, gestures or threats, or self-mutilating behavior
6) affective instability due to a marked reactivity of mood (e.g., intense episodic dysphoria, irritability, or anxiety usually lasting a few hours and only rarely more than a few days)
7) chronic feelings of emptiness
8) inappropriate, intense anger or difficulty controlling anger (e.g., frequent displays of temper, constant anger, recurrent physical fights)
9) transient, stress related paranoia or severe dissociative symptoms
Lindahand is correct in saying that bipolar mood episodes aren't fleeting things that can change from moment to moment like that, even if you happened to have a rapid cycling form. Episodes of mania and depression involve much, much more than just feeling angry or happy; there are a host of physiological and mental changes that come along with these emotions, such as dramatic sleep changes, racing thoughts, disproportionate feelings of grandiosity or worthlessness, etc. etc. etc.
Keep in mind that a trained mental health professional should be the one to make the judgment about whether or not you are experiencing a form of bipolar disorder (that is, don't take our word for it). Regardless, it does sound like you should really consider talking to a counselor about these problems because of the effect that they are having on your personal relationships. You might even want to look into group or family counseling.
My personal advice is to avoid medication if you can. Therapy can be really, really powerful. Good luck!
Bipolar moods last longer than minutes. Even if you have ultridian rapid cycling (changing moods several times a day) It isn't usually a flip back to normal so quickly thing (others please correct me if I am wrong on that - its just my experience as an ultridian cycler), and the flip back to normal isn't influenced by social settings. If you can control yourself in public situations probably not a bipolar thing. But what you describe is serious and if it doesn't fit this category it may fit another one. Bottom line is see your GP or a psychiatrist. If you think you will chicken out by not being honest print this post and take it in with you. This is the criteria for diagnosing bipolar disorder
Bipolar I Disorder--Diagnostic Features (DSM-IV, p. 350)
The essential feature of Bipolar I Disorder is a clinical course that is characterized by the occurrence of one or more Manic Episodes or Mixed Episodes. Often individuals have also had one or more Major Depressive Episodes.
Bipolar II Disorder--Diagnostic Features (DSM-IV, p. 359)
The essential feature of Bipolar II Disorder is a clinical course that is characterized by the occurrence of one or more Major Depressive Episodes accompanied by at least one Hypomanic Episode.
Criteria for Major Depressive Episode (DSM-IV, p. 327)
A. Five (or more) of the following symptoms have been present during the same 2-week period and represent a change from previous functioning; at least one of the symptoms is either (1) depressed mood or (2) loss of interest or pleasure.
Note: Do not include symptoms that are clearly due to a general medical condition, or mood-incongruent delusions or hallucinations.
depressed mood most of the day, nearly every day, as indicated by either subjective report (e.g., feels sad or empty) or observation made by others (e.g. appears tearful).
markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day (as indicated by either subjective account or observation made by others)
significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or decrease or increase in appetite nearly every day.
insomnia or hypersomnia nearly every day
psychomotor agitation or retardation nearly every day (observable by others, not merely subjective feelings of restlessness or being slowed down)
fatigue or loss of energy nearly every day
feelings of worthlessness or excessive or inappropriate guilt (which may be delusional) nearly every day (not merely self-reproach or guilt about being sick)
diminished ability to think or concentrate, or indecisiveness, nearly every day (either by subjective account or as observed by others)
recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide
B. The symptoms do not meet criteria for a Mixed Episode.
C. The symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.
D. The symptoms are not due to the direct physiological effects of a substance (e.g., a drug of abuse, a medication) or a general medical condition (e.g., hypothyroidism).
E. The symptoms are not better accounted for by bereavement, i.e., after the loss of a loved one, the symptoms persist for longer than 2 months or are characterized by marked functional impairment, morbid preoccupation with worthlessness, suicidal ideation, psychotic symptoms, or psychomotor retardation.
Criteria for Manic Episode (DSM-IV, p. 332)
A. A distinct period of abnormally and persistently elevated, expansive, or irritable mood, lasting at least 1 week (or any duration if hospitalization is necessary).
B. During the period of mood disturbance, three (or more) of the following symptoms have persisted (four if the mood is only irritable) and have been present to a significant degree:
inflated self-esteem or grandiosity
decreased need for sleep (e.g., feels rested after only 3 hours of sleep)
more talkative than usual or pressure to keep talking
flight of ideas or subjective experience that thoughts are racing
distractibility (i.e., attention too easily drawn to unimportant or irrelevant external stimuli)
increase in goal-directed activity (either socially, at work or school, or sexually) or psychomotor agitation
excessive involvement in pleasurable activities that have a high potential for painful consequences (e.g., engaging in unrestrained buying sprees, sexual indiscretions, or foolish business investments)
Criteria for Hypomanic Episode (DSM-IV, p. 338)
A. A distinct period of persistently elevated, expansive, or irritable mood, lasting throughout at least 4 days, that is clearly different from the usual nondepressed mood.
B. During the period of mood disturbance, three (or more) of the following symptoms have persisted (four if the mood is only irritable) and have been present to a significant degree:
inflated self-esteem or grandiosity
decreased need for sleep (e.g., feels rested after only 3 hours of sleep)
more talkative than usual or pressure to keep talking
flight of ideas or subjective experience that thoughts are racing
distractibility (i.e., attention too easily drawn to unimportant or irrelevant external stimuli)
increase in goal-directed activity (either socially, at work or school, or sexually) or psychomotor agitation
excessive involvement in pleasurable activities that have a high potential for painful consequences (e.g., engaging in unrestrained buying sprees, sexual indiscretions, or foolish business investments)
C. The episode is associated with an unequivocal change in functioning that is uncharacteristic of the person when not symptomatic.
D. The disturbance in mood and the change in functioning are observable by others.
E. The episode is not severe enough to cause marked impairment in social or occupational functioning, or to necessitate hospitalization, and there are no psychotic features.
F. The symptoms are not due to the direct physiological effects of a substance (e.g., a drug of abuse, a medication, or other treatment) or a general medical condition (e.g., hyperthyroidism).
Episodes of extreme anger and having difficulty relating to people at times can be part of bipolar but it would depend on what else is going on. It definitely would be worthwhile speaking to a therapist and seeing if a further referral is needed.