Firstly don't panic, if you have difficulty paying go straight to the Mortgage Company to discuss, they are more likely to help you that way. Look at interest only for a short period, or extending the term with a promise to catch up in the future. If the worst case scenario happened, the property would be sold and they would keep the amount outstanding on the mortgage plus any fees involved and you would get any equity remaining.
If in negative equity unfortunately you would still owe them any outstanding debt. Mortgage Companies do not like to repossess and you should be able to come to some arrangement.