Definitely see your doctor. You have to weigh up the possible damage that pills might do to you against the damage the depression will do to you. With each episode of depression your risk of suffering heart problems later on increases. And I'm sure it comprimises you immune system and makes you more vulnerable to all sorts of other illnesses.

If you are really against taking anti depressants, or find them of limited help, ask your doctor about referring you for cognitive therapy, which has been shown to be equally effective and may be more helpful in preventing further episodes.

Otherwise, as others have said exercise, and trying not to cut yourself off, and trying to keep doing anything you still find enjoyment in, are all useful in minimising the depression.

PS. I sympathise with you a lot. How you describe yourself at work sounds exactly the way I am when I am depressed. One thing I would say is that taking some time off sick really can help (as long as you dont sit at home worrying about work), especially if you have a sympathetic boss that will cut you a bit of slck and ease you in gently when you return. Often just having someone know about it really eases the situation and stops you getting so tied up in knots.