Sounds like those smaller tongue and groove tiles that they still sell, rather than the "office style" 2x2 or 2x4 panels (which would probably look hideous in a main bathroom). From my experiences, sometimes those are not really "dropped" much from the underside of the joists. They are usually stapled/glued to furring strips that are attached to the joists due to their smaller size. I believe they are a gypsum product (?). If the ceiling is in fact dropped a bit below the joists and you are trying to gain extra headroom, you could pull a few down and see what's above them. A lot of times dropped ceilings hide conduit, water/gas pipes, etc. so who knows what's above it. The small tiles are usually soft and can be removed easily, however some of the surrounding tiles may be damaged if you're not careful. They are probably tongue and groove. Hopefully this helps, but it's quite hard to give ideas without actually seeing the subject in question.