Sacred Haven of Debauchery

How are depressive states related to insomnia and simply feeling sleepy?

Lack of sleep. And a lack of sunlight.
And sometimes, living by a strict schedule for a couple of months can help with depression.

Is it normal that I heat up yogurts on a heater?

Using items for purposes other than their intended use is a sign of creative thinking, so whether it's normal or not, I don't know, but it's definitely good.