answer:I would have thought that it would have left your lungs by now, but I guess its possible that you may have some residual gas left. However your correct to believe that helium could do this especially since its an inert element thus could technically suffocate you if there were enough of it in your lungs. The only thing that gets me though is that helium is lighter than oxygen, so by the time your squeaky voices go away, the helium should be gone from your lungs. It’s possible that there’s something else in your environment, or that (depending form the size of these balloons) your muscles suffered (a lot) from the lack of oxygen and were still in the process of recuperating.