How to work when dealing with greif?

My grandma passed last monday, and I’ve been turning to unhealthy habits to cope. I wanna be better, for myself and for my mom. I have no motivation whatsoever to work on school assignments, I just keep getting up at 6am grabbing my skates and not coming back till late at night. I’m barely eating or sleeping it just feels wrong to. I feel guilty for feeling sad, I feel guilty for feeling happy, I just can’t win. When I am home I just lock myself in my room and get so hyperfixated with reading, doing anything else seems impossible.
How do I function normally when my mind is in a fucked up state?