Yes, this sounds like pretty classic hypoglycemia. The difference between this condition and diabetes is this: in Diabetes, the body's pancreas does not make enough insulin to covert carbohydrates that are eaten into energy. Without insulin, these sugars build up in the bloodstream and the person becomes ill. In Hypoglycemia, the pancreas makes too MUCH insulin at times, and this overdose of insulin, if you will, causes the symptoms you describe. You will find that eating something that has some carbohydrates in it will make you feel better quicker than something that is low in carbohydrates when you feel this way.
Many people exeperience this and there can be many causes. Some of these are waiting too long between meals, exercise which burns up sugars in the body and speeds up metabolism (and also insulin production), eating foods very high in carbohydrates (which overstimulate the pancreas and cause a hypoglycemic episode shortly after eating the high-carb food, or even in the case of one close friend, taking vitamins containing chromium triggered hypoglycemic episodes until the vitamins were stopped. So you would be wise to look for possible triggers to these episodes and see if you can stop the trigger instead of simply treating the episode. It is probably not dangerous unless you are one of the rare folks who actually loses consciousness, but it certainly makes you feel awful and it can affect reaction time when you are driving a car.
Please check out my statements with your family doctor, for I am NOT a physician, but am a long-time, well-educated type 1 diabetic who gets asked about hypoglycemia a lot. There is no proven relationship between hypogclycemia and diabetes, although some doctors think that perhaps some people who suffer from hypoglycemia and don't treat it to stop it from happening may perhaps over-use and wear out their pancreases in time, and may eventually become type 2 diabetics. There is no proof to that statement, but it is a theory that some have stated.
The current low-carbohydrate diet fad seems to be one way that modern doctors tend to treat chronic hypoglycemia, for some people tend to stop having the hypoglycemic episodes in time after cutting back on their total carbohydrate consumption, for carbohydrates cause the pancreas to produce insulin. If this happens only rarely, then drink a small cup of juice when you feel bad and don't worry about it. If it is a chronic problem, then perhaps you should get a glucose-tolerance test run by your doctor and seek some dietary treatments.
Diabetic people often have thyroid problems too, although the two are not connected in function, but both are hormone-producing organs. Your symptoms do not sound like thyroid problem symptoms to me, but check with your doctor.