For me I sometimes fall asleep to undergrad math problems, the more challenging ones. By then, I'm too tired to want to write things down (since that will wake

For me I sometimes fall asleep to undergrad math problems, the more challenging ones. By then, I'm too tired to want to write things down (since that will wake me up), so it's really hard to make actual progress, or thoroughly plan out the formal steps required to verify a proof approach. So I just keep turning it over while trying to keep everything in my head. The focus required stops my mind from wandering and getting distracted.