Perhaps, though not really. Commercial aircraft generally accelerate at takeoff at around 2-3m/s. For most people, that is quite enough, and that only gets you to 140kt. By comparison, doing 1g for 5 seconds (being generous) only gets you to 95kt. So you aren't really going to be able to get much flight out of that. More realistically, a gun would have to accelerate you to nearly the speed of sound or more. Mannned rocket ships have a (throttled) peak acceleration of 3G, so that sets a realistic upper bound and probably way over what might be considered reasonable. I've read that the Willis tower elevators accelerate downward at 8m/s and that is uncomfortable and just for a short time. It's likely the case that such acceleration would feel better if one were lying down. It's a curious question.