A similar situation happened with Chubbz and I
He was asleep for 2 months but instead of going to sleep while I went on vacation he woke up the day i was leaving.
I had to scramble to get his food and tank set up for him it was quite hectic. lol
He was all right though.
I did nothing different for him to wake up.
The only thing i could think of was that he sensed the pressure in the air.
The day we left we had massive amounts of rain and thunder.