You know how sometimes you can set up an automatic email response when you are on vacation to let the sender know you are out of the office or away? How about coming up with a similar message to copy and paste to your friends when you are struggling?
" Thank you for your message. I struggle with ____sometimes and this is one of those days. I wanted you to know I got your message and appreciate you reaching out. I will respond as soon as I am feeling better"