This Vertigo song makes dizzy, it may be that.
OK just kidding because I have no idea beyond see an ORL.

However, it is pretty much beyond home cures. It might be caused by a medication, but unless he falls down sometimes as a result, the best solution is probably to ignore it. If he does fall, or if it is getting worse, he should see a doctor.

That's about all I can think of. It just depends on what's causing the dizziness. If it's a mechanical problem in the inner ear (I have one of those) there's very little to do except avoid dangerous situations when it happens. In my case I'm lucky that it's only an intermittent problem and it usually only affects me when I'm lying down--but I'm still not too eager to be on stairs on those days.

If it's caused by something else, like an infection or a problem in the brain, there might be medications or therapies to try.

Mind you, I'm not a doctor--I don't know if anyone here is. If it's something that's interfering with your friend's life, they should ask a professional. If it is something really serious, we can't help.

~Neshomeh