We all have bad days. Those of us with depression and anxiety will have heightened or 'exaggerated' feelings.  A bad day will feel really  bad. Everything seems so black and sometimes it's a struggle to get out of the hole. You may think 'what is the point?' and 'why bother'. Other days may not feel as black and you enjoy life. This is why people may not understand what you are going through. They may see you on a good day and think 'she/he is fine'. I'm currently trying to r