Muscle strain and soreness is more likely if

When you don't exercise enough, don't exercise at all  or if you just don't exercise properly. This is because the muscles need training and if they are not used in a while, then will get the idea that they are not needed. that is why, when exercising, the body needs to be pumped up so that the muscles are too.   

If you exercise or are active without stretching before hand

The physiological benefits of warming up and cooling down

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