Find a great Realtor that is looking out for you. Waiting for the bank will likely just put you into default, They will accelerate the mortgage and file for foreclosure. They may offer you a loan modification, but it will likely require you live in the home.
You should initiate the short sale by having a consultation with a Realtor that can help you assess the true market value of the home. Once you know this, there are programs such as HAFA, that regulate some short sales. Either way, you should get the home on the market.
A short sale negotiator would likely be a waste of money in your situation. Most Realtors still in the business have a good handle on the short sale process. I attached a ink to the HAFA program for you to view. Interview a few Realtors. Find the one who demonstrates a strong understanding of your situation and the short sale process. You listing agreement with your agent should have provisions for bank approval on it. They should also compile a series of documents with you to submit to your bank. These include a hardship letter, bank statements, income docs, etc.
Once you have a rock star Realtor, get an attorney to provide you with a clear understanding of deficiency judgements and any legal clean up that may need to occur. This should be done before you agree to the terms of the short sale with your bank. You should also check with a CPA to make sure to have appropriate exclusions for the 1099 that the bank will likely send you for any deficiency.
Best of luck. This is becoming a routine process, so relax, exhale and get it done. Don't be intimidated or coy, just start moving in the right direction.
Chicago Consulting Group