I believe there are differing opinions out there on this subject, but I do not think a short sale will have a huge impact on your credit history.  If you can do it, you are merely entering an agreement with the lender to accept a lesser amount than is owed on the loan as payment for the entire debt.  Accordingly, it may be reported as "Paid - Settled" which is, technically, an adverse report.   However, that is much better than a default or foreclosure.   Once the short sale is completed, the mortgage will be discharged in the usual manner, with a filing at the registry of deeds.

Two things to consider, however.  First, if you have missed any payments on the mortgage, or miss any prior to the short sale, that information will most likely appear on your credit report, and your credit score will take a major hit.  Second, short sales can be somewhat complicated, and there is often a lot of negotiating that goes on between the home-owner and the lender.  For example, it may be possible to negotiate with the lender about how the sale will be reported to credit reporting agencies.  Because that information can be crucial to your future credit health, and because time is usually of the essence in these 'emergency" deals, I would try to find a MA real estate attorney to help set up the short sale.  If the sale and documentation is structured properly, the attorney's fees can be paid out of the sale proceeds.  Good luck.