You are entitled to take care of yourself, RG. No need to feel guilt or shame over it. It takes some getting used to, though - not feeling guilty about making your needs a priority. (It did for me, anyway.)
I found this little exercise helpful. Articulate what it is you feel guilty about and then add "...and that's OK" to the end. Then say it to the mirror five times.
I feel guilty because I don't want to go to a bar with my husband and some friends, and that's OK.
I found it to be helpful.