I know this is like a circle you can't escape from.
I don't have a general solution to that one, there are multiple things you can try.
One would be exagerating your worry so much that we will realize that it cannot be that bad. Another would be finding someone to talk to about those sad thoughts and empty your bucket so you can fill it with happy ones. You can read my previous articles about emotional equations, depending on the source of your sadness you can find there some insights