An example of a phobia is: a mother worries about her child walking to school.
a person is afraid to take drugs for fear of an overdose.
a person kontinues to believe that something has not really happened.
a person panics in elevators and therefore avoids them.

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