Depression is a stage of grieving in which

Emotionally upset and acting very different

One may feel hopeless, and a deep sorrow for their loss. It is extremely important to talk with someone about your feelings over your loss.

Warm up, exercise, cool 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