Focus on things you can control, such as the quality of your work, your attitude and whether you choose to continue working for the merging company or start a search for new opportunities. You always have choices. At any time, you can leave the company for a better opportunity, including temp work if your dream job isn't readily apparent. Risking your health and well-being to cope with a bad work situation simply isn't worth it. Make use of the free counseling services and stress workshops.
Many companies provide free counseling for individuals during merger situations.
If your company does, make use of it to figure out how to cope with your situation. If this isn't an option, many hospitals and community centers provide free stress workshops. Public libraries or the internet are other sources of useful information on how to manage stress. Exercise, meditate, find quiet time for yourself. Find time to unwind in a manner that pleases and calms you.