Second, recognize that an acquisition is a change of life - that can certainly make one feel anxious and depressed, no matter how much you may have looked forward to this milestone.
Third, nobody is indispensable. If you died in a car crash today, the company would find a way to continue.
In your place, I'd go through with the acquisition (and do my duty to my investors & employees). When the dust settles (3-6 months), I'd go to my Board of Directors and tell them I need to change roles at the company. That would include dropping all my day-to-day responsibilities and dropping back from full-time. Be explicit that you're on a transition out of the company, and you want it to be orderly (for the company's benefit) and time-limited (for your benefit). When the time expires, leave with thanks and go live your life. Good luck and congratulations!