I had a 400 someodd gram male go off feed for about four or five months or something, ages ago.

Your snake is fine. let the weather warm up.

When you say lethargic, do you just mean, hanging out in a hide. not doing anything? Ball pythons.... generally like to stay in one spot. ive got several animals that will just sit.... for days and days in one hide or the other.

When you take the snake out of the enclosure, does the snake move around and try to find a place to hide? or just chill with you?

lethargic, is more of a word for, having trouble moving, and otherwise looking sickly. Not for a snake that is quite happy to be curled up in a warm spot, and just never moving.