Vertigo can have numerous causes, so that's unfortunate.
One type, benign paroxysmal positional vertigo, is characterized by brief episodes triggered by changes in head position vs. gravity in the absence of other causes. E.g. lying down.
In this test, the doctor (the older man with the white hair, obviously) is testing the right side: he turns the patient's head 45 degrees to the right, and then quickly lays her down. Nystagmus occurs; you have veritgo!
What is happening?
God decided to make those canals be orthogonal-- the horizontal canal laying horizontally, and the other two vertically separated by 90 degrees. They are filled with fluid, which swish around as you move. In essence, the swishing is what the brain reinterprets as movement.
Little calcium carbonate crystals (otoliths) dislodge from the utricle and fall into the posterior canal. Now you have a little rock in your fluid filled tube, which causes all sorts of swishing on its own. Now you have vertigo.
Gravity is the key. Since the posterior canal is the most likely place for the crystal to go, and the posterior canal is mostly upright, the biggest effect of the swishing crystal will be when you lie down (and it is free to move.)
What do you do about it?
There are several maneuvers used to literally roll the crystal out of the semicircular canal. Here's one:
Steps in and 2 are just like the test.
Step 3: turn the head 90 degress to the unaffected side, and hold for 30 seconds
Step 4: then turn the head (and body) another 90 degrees so the head is face down (not well depicted in this drawing)- hold for 30 seconds
Step 5: sit up.
One study found the awesomeness of this maneuver to be 88% vs. sham maneuver 26% one month after treatment. Not bad for no meds.
Keep in mind the body position is irrelevant, what matters is accurate head positioning. The crystals are very sensitive to the force of gravity, so the more accurately you can move the head, the better. NB: this maneuver is will cause the very veritgo you're trying to treat, so bring a bucket.