How do you stay in control when you can feel yourself losing it?

I was starting to feel a lot better after a few problems and almost a month of taking prozac but tonight I can feel myself teetering on the same edge as when I tried to take an overdose before I started the prozac. I am aware of it but so was I before and I still did it. What do you do when you feel like this (apart from calling the samaritans - I'm not into that)?