I've only tried it thrice, the only real rough ride I got was on a middling dose, a low dose is decent if you want a buzz. (And don't have booze...which is a lot easier on your body.) A high dose (up around 750mg for my body weight, ymmv.) is another animal entirely. It's a really intense disassociative trip, worth trying if you've never done anything similar, and really imo the only real reason to ever use dxm. The effects of the first two plateaus are achievable pretty easily with other substances that won't make you feel like a big bag of shit.
However much you choose to do you're well within the safe zone, so don't worry too much about it, so long as your pills don't contain any other active ingredients besides dxm. Just be aware that if you have stuff to do tomorrow you will have a hangover pretty much all day, it's not so bad but you won't want to operate any heavy machinery.