When you’re someone with a side project, you will have less “free time” than someone who doesn’t have one. You will have to work many weekends and holidays. But you still deserve a break every now and then!
Make sure you take purposeful breaks. Decide on the time off and refrain from working during it. Take a break fully! Work hard; rest hard.
When you’re feeling overwhelmed and stressed about the things you haven’t done, go through what’s worrying you and consider how much of a priority they really are. Often things are important, but not urgent.