Not necessarily. In most circumstances there's no duress since a patient can visit a different physician. The case of someone who is in severe pain, has already waited 3 days, and has every reason to think that he might need to wait another 3 days if he opts to see a different physician is an exceptional one.

(And even in the absence of a contract, there's a quasi-contract, so a finding of duress wouldn't obviate the requirement to pay for services rendered.)