Is selective mutism self diagnosable?

I’d say you can see if someone were to have many of the signs, however to be sure they should go get a doctor’s opinion

Diagnosis should be made by a professional familiar with selective mutism who can rule out other conditions that present similar symptoms.

Because without physical activity, the body has extra "energy" if you will, and so when it is time for bed you are not tired, so you end up staying up all night. also there is probably an effect on your internal clock, which messes with your melatonin production which goes hand in hand with your sleep cycle