I got this idea from Universal Mind. Lately I've been trying to float as a reality check. Sometimes looking at the clock too much isn't a good idea because people will think you're bored. Holding your nose is weird in public, and even looking at your hands can be a little obvious if you do it too often. The internal breathing block is OK, but I'm afraid that is too subtle to work in a dream.

Trying to float works in any situation; sitting, walking, even driving, and is totally unobtrusive. I've floated lots of times in lucid and non-lucid dreams, so I'm pretty sure it will work if I remember to try it in a dream.

Hopefully I'll get the chance soon.