You didn't mention before that you were ill with a glandular infection for two weeks prior to the pins and needles feeling starting in your finger tips and spread though out your left arm whilst driving home...
Due to your age group and the saliva gland infection (typically include symptoms of saliva gland swelling, soar throat, dry mouth, pain swallowing, fever), and your mentioned symptoms of fatigue, chest-breathing issues, and muscle related issues, it's very possible you've been dealing with the Epstein-Barr virus (EBV) which typically starts off with saliva gland involvement.
The Epstein-Barr virus (EBV) is the main viral cause of mononucleosis, otherwise known as mono, glandular fever or the kissing disease because infection is primarily spread through saliva and its a very common viral infection in teens and young adults.....Mono is primarily diagnosed based on symptoms but can be confirmed with blood tests for specific antibodies though its not always accurate depending on the timing of the test.
Generally the blood test will be negative during the 4–6 week incubation period, the highest amount of antibodies in the blood test only occur for 2 to 5 weeks after the symptoms start but some people get mono and have no symptoms at all, whilst others feel like they've been hit by a mack truck of symptoms...up to 95% of people have had an EBV infection by the time they are adults.
IF your nerve conductor test, neurological assessment and MRI's are NOT abnormal it is 'highly unlikely' that what you've experienced has anything what so ever to do with a neurological condition like MS or a fatal condition like ALS (which btw most people who develop ALS are between the ages of 40 and 70) and highly likely this has had everything to do with your initial gland related viral infection.
Googling symptoms and reading about MS and ALS has probably triggered you to become unnecessarily anxious about your health during the typical viral symptom time frame (which can take anywhere up to 3 months to recover from depending on numerous factors), and a high level of anxiety is a common cause of a 'disconnected feeling' and experiencing all over random muscle twitching, which would also help explain why that's continued after the initial symptoms you started off with have been resolving....I'd recommend you consider seeing a therapist to help you get back on track!
I hope that helps.......JJ
Prednisone is prescribed for many different types of issues, basically anything from an allergic reaction, Bursitis, Migraines, Cluster headaches, etc all the way to chronic diseases, cancers, organ transplants but it comes in different forms and doses depending on the medical situation.
Sometimes the immune system doesn't settle back down after it's been activated and a low dose, short course of oral prednisone (which is a synthetic glucocorticoid ie steroid), will help to suppress the immune system and inflammatory response and get it back to it's normal state until it's needed again.
Keep in mind that it's not uncommon to treat symptoms without having an identified causation (idiopathic), there isn't always a condition to explain the symptoms and when symptoms are seriously effecting quality of life it wouldn't be in the best interest of the patient to prolonging getting symptom relief if the treatment would be the same-similar dx or not.
May be the thing you need to be considering is how problematic this has all been and whether or not it's worth it to you to give the medication a try or give it some more time...
Hope that helps....JJ
Steroids won't do anything for the issue your most bothered by if the feeling is of being disconnected from your body, which if we're speaking the same language, as i've mentioned before is most likely due to a psychological issues ie your health related anxiety...
"Anxiety causes the body to produce the stress response (also known as the fight or flight response). The stress response stresses the body. When the body becomes overly stressed, which we call stress-response hyperstimulation, the body can exhibit a wide variety of odd and unusual sensations and symptoms. This feel wrong, odd, strange symptom is one of them.
You, or parts of you, feel wrong, different, foreign, odd, or strange. It could be your entire being or body, one part of or spot on the body (such as an arm, leg, foot, hand, finger, cheek, lip, tongue, or any other part or spot on the body), or any portion thereof.
This feel wrong, odd, strange symptom can persistently affect one area only, can shift and affect another area or areas, and can migrate all over and affect many areas over and over again.
This feel wrong, odd, strange symptom can come and go rarely, occur frequently, or persist indefinitely. For example, you may feel a pins and needles feeling once in a while and not that often, feel it off and on, or feel it all the time.
This feel wrong, odd, strange symptom may precede, accompany, or follow an escalation of other anxiety sensations and symptoms, or occur by itself........."
btw what do you mean by a stiff index finger and other joints being kind of stiff and whilst you thinking about that, also think of what activities you have been doing that might explain it eg wake surfing, sitting in a bean bag playing the ebox all weekend, shooting hoops etc etc etc
Hope that helps....JJ