Sometimes friends think that by taking days to call them back it means that I have worked out what the problem is.

What worked for me was ansering my phone when I know it is one of my friends and telling them right out "I am not feeling good right now" because I am not waiting for days to tell them this they right away ask me if there is anything they can do for me or they come over and we talk or we make plans to meet somewhere so that we can talk about what is going on with me. Like one friend told me days later there is noting they can do to help me figure out the situation but right when I am going through it there are many options that they can help me with.

So suggestion - let them know when its happening not days later after the situation has happened and there is nothing they can do but say "glad you are feeling better enough to call them back" because the action of you are calling them later gives them the idea you are doing better especially since you don't answer the phone in the beginning of slipping downhill. Its hard to make that switch from asking for help after the fact to asking for help as its unfolding but I can tell you from experience the outcome is much better because I now get the help and understanding from my friends that I need when I need it.