A good start would be to stop calling yourself a depressed mental idiot.
Every time you say that or think it, you put yourself down a little more.
Even if you don't believe it, call yourself an intelligent, normal human being. You're clever enough to ask how to help yourself, aren't you / So you cannot be an idiot or 'mental'. If you do that, even if you don't believe it you won't be making yourself feel any worse.
If you've got SAD, what is your Gp/specialist advising ? There's lots of different medications available , but if you want to avoid that, ask them about light treatments. You can get special lamps which give you the extra light that is very helpful to some SAD sufferers.
Try to keep active , even if you don't feel like it. Keep a routine to your day. Keep a diary listing your achievements and re-read it. Generally look after yourself, eat healthily and exercise gently if you can.
Hope this helps.