The housing market's collapse is forcing a growing number of Americans with large medical bills to choose between paying the mortgage and paying the doctor. People have long resorted to borrowing against their homes to pay for medical care in times of unexpected illness or after an accident. But with home values plummeting and interest rates on adjustable mortgages ratcheting higher, some indebted patients are at risk of losing their homes in order to pay for big-ticket medical expenses. Other patients are forgoing healthcare in order to keep from losing their homes.