You must be this tall to ride this roller coaster...?
In all seriousness though. Its a piece thats meant to catch your attention, but little after that. Suicide rollercoaster is just sadistic, like Rollercoaster Tycoon sadistic.
I'm also not a doctor, not yet atleast (stealing docterates is hard), but doesn't it take more than just a few seconds of going without blood for your brain to die? Thats one long rollercoaster you'd have to make. What if I, by some freak accident, survive. The rush of blood back into my head will NOT be euphoric - as opposed to a needle, which just puts a bit more poison into your blood.
What about cost? Practicality? If you are granted this, you're in a fucked up situation. Most people who would qualify would be bed bound, probably on life support machines, are in a coma, or any other host of medical reasons that won't allow you to get out of bed. Getting up, into the seats, then starting the ride up, and hoping it will work would probably cause the patient more pain that the euphoric ending you promised.