Thing to remember is everyone has their own way of dealing with it and the key is finding the right way.
I was having a rubbish time a fair few years ago - I was in a job I hated and couldn't see anyway out of it. I went to see my GP but he was on holiday so I saw the Locum instead. He said I wasn't the first from my workplace he'd seen to have the same sort of issues and asked me whether I wanted anything to help. I said that I didn't want drugs as this would be masking the probelm, not dealing with it.
He then gave me the best piece of advice I've had for feeling down. He gave me a 2-week sicknote then said "Right - I want you to do whatever YOU want to do during this time off. Try and find a different job if you can, but the rest of the time, do what you enjoy". I ended up up House-sitting whilst my brother was on holiday, had the house to myself and had no issues with anyone trying to call me coz no-one knew the number. My mobile was switched off. It was awesome. I put my CV in with an agency where they lived and then moved in after 4 weeks as I had got a new job. It was EXACTLY what a needed - a fresh start.
Not saying it'll work for everyone but you need to change your routine.