Work to live, don't live to work.

If you feel that taking on a certain roll will cause you more stress than you can sustain, its not it. The last thing anyone needs is stress to tip you into an episode. Learning to live with what you can sustain and not what you are capable of is hard. You may well be able to do the job and do it well, but in order to be stable you need to be happy with a lesser role. As long as you can afford it, I'd chose a happy stable life over a promotion anytime. Let someone else take the stress, enjoy your life.

Just my two cents worth from someone who's been there, burned out and then had to pick up the pieces afterward. My Conclusion - it wasn't worth it.