I read something the other day and it really stuck with me. It said "I am allowed to say no to others and say yes to myself".
When I was speaking with my counselor a couple weeks ago, she explained to me that you can't give when your pot is empty. Sure you can try, but you're not giving your best to yourself or to others when you're running on fumes. Just like when you're flying and the flight attendant reminds everyone in the event of an emergency to put the oxygen mask on yourself prior to helping anyone else. I think a lot of us feel as though we need to help as many people as possible, or help anyone when they ask, completely disregarding what it is doing to our own mental health.
Sometimes, we have to step back and realize that we can't run on empty. We have to refill our own tanks before we can even consider helping someone else.
It's perfectly fine to tell someone No.