'Feeling Good, the New Mood Therapy' by Dr David Burns is totally amazing! No other self-help book comes near this book IMO. Doesn't just tell you why you get depressed but gives you really simple exercises (CBT....the first CBT book ever written) you can use straight away that really work quickly, lifting your mood. So easy to read as the author writes so well and seems so lovely, kind & has a great sense of humour. I went down the self help book route about 5 years ago, after asking for CBT on the NHS, but being told there was 1 year waiting list & I'd only be put on the list if I agreed to take anti-depressants. Private CBT therapists were charging £80/hour which I couldn't afford. BEST BOOK I've ever bought, changed my life.