The authority of a stackexchange thread notwithstanding - ER and urgent care visits are what happens when primary care physicians cannot accept same-day consultations with patients. By all means try to call your primary doctor, but if they can't see you that day I would ask them if the prudent course of action is to seek immediate medical care at the ER or urgent care.
Yep, I passed out just after a surgery so I went to the ER. If it was before 5:30 I'd had called/visited my doctor. If I had arrived at 9PM instead of 9:30 I would have used the urgent care. So I went to the closest medical services in 200 miles.
