Using an inert gas cylinder on its side, say lying on the floor beside you, should be fine. Most true gas cylinders should be fine, in fact --consider that scuba divers are using air tanks trapped to their backs, most often in a horizontal position.
The reason some people say, "oh, NEVER use a tank on its side!" is because there are two common types that you must not use horizontally: propane and acetylene. This is because both of those gasses are stored in liquid form; the one as liquefied propane and the other in solution, in acetone. For inert gas, however, it shouldn't be a problem.