1. Sexy doctors ride motorbikes.
2. Every hospital team includes one wisecracking, insensitive, immature jackass with a (well hidden) heart of gold. This jackass is probably the smartest doctor on the team, so if someone's unforgiveably rude to you when you're lying in ER, suck it up. He's going to save your life. Contrariwise, if nobody's mean to the patient, you should worry; the jackass might be having a good day, which means he's lost his edge and is about to make a fatal mistake. On you.
3. You will not get better until you have resolved your complicated family issues, so you may as well call your mom/ex/former best friend right away. Speed things up.
4. Diagnosing and/or treating a complicated ailment works on exactly the same principles as solving a crime. It can't be done without friction (possibly of the literal, sweaty kind) among colleagues, a series of red herrings, and a hefty dose of rebellion against the dictatorial boss who inevitably fails to see the truth of the jackass's way out theory (or alternatively, the need for radical experimental treatment by the underqualified interns).
5. Hospital visitors wear a lot of really great knitwear. In this they are superior to witnesses and to relatives of murder suspects. It's probably because of their increased need for comfort. Or maybe hospitals are just colder than police stations.
6a. Contrary to popular opinion, doctors do not shag nurses. They shag each other. All the time.
6b. It is theoretically possible for doctors to have romantic interests outside of work (we know this because they occasionally get divorced), but how this should actually develop is a mystery, because they never actually meet or date anyone except each other. Actually they don't really date each other either. They just shag in the supply closet.
6c. Terminally ill schoolgirls are remarkably adept at wheedling inappropriate kisses out of doctors who really should know better. Interns are smarter. They don't fall for that crap.
7. It's never lupus.
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* House, Grey's Anatomy and, er, Green Wing. Okay, it's not a drama, but same diffs. It's possible that ER would completely contradict every lesson here... but I doubt it.