How can I stop feeling guilty because the house is messy?

It isn't wrong. It might be helpful to consider whether you are violating anyone's rights with your messy house. If not, there is no reason to feel guilty. Your house is messy because you've been doing other things. It's a choice and it's ok--it doesn't mean anything to have a messy house. If you'd prefer to have a clean house you'll need to adjust your schedule. It's up to you.
Depends. Dust bunnies have never attacked anyone. If its minor clutter don't sweat it. If your house looks like an audition for "hoarders" contact a physician--this can indicate a possible disorder which can be treated. Good luck!