I was SUPPOSED to have the test, but the doctor I was referred to decided I just needed more sleep and to disregard my regular doctor's request.
Anyway, the tilt test is really to see if there are any problems with blood-pressure, or what is techinally known as neurally mediated hypotension. It's when your BP drops more than it should when you stand up for instance. They strap you to a table which, as the name indicates, tilts. They lie you flat for a while, then tilt the table up to see if your BP is affected at all. They may also inject adrenaline to see if the BP reacts normally to "stress" (ie. like when you exercise). My stepmother had this test, and although her BP was OK, they found the part of the brain which is meant to make your heart-rate increase wasn't kicking in which is why she was having black-outs when she stood up sometimes.
If your BP is low, or not increasing as it should when required, they may prescribe sodium tablets to increase the BP. My cardio suggested I increase my salt intake (in general) to see if it helped with my dizzy spells, which it has - although I tend to have a pretty low salt diet at the best of times, so I wouldn't just do this without talking to a cardio first. In general my BP has gone up from around 90/50 to 110/65 which has been just enough to alleviate the dizziness.
If you type in "tilt test" or "neurally mediated hypotension" into Google, you should find some really helpful information.
Cheers
Anna : )