You can float and be buoyant, but stay in place. There’s a sense of lightness and buoyancy, so keep that sense of lightness, but stay where you are.

"Breathe in such a way that there’s no holding on, so that things are allowed to flow smoothly. The breath flows smoothly, the blood flows smoothly, and there’s a sense of ease all the way through the breathing process.

Some people at this point begin to get a sense of floating, but try not to drift out. You can float and be buoyant, but stay in place. There’s a sense of lightness and buoyancy, so keep that sense of lightness, but stay where you are. You’ve learned to breathe in such a way that the whole body feels at ease throughout the in-breath and out-breath. Try to maintain that sense of awareness of the whole body, and let the pleasure radiate out through the body. Just learn how to maintain that, to stick with it. If you find yourself losing focus when you open up your range of awareness to the whole body, go back to surveying the body spot by spot, section by section, and then try settling down with the whole body again. You may find yourself going back and forth like this for a while until you feel comfortable and stable staying with the whole body. Even though there’s a sense of ease and lightness, there’s also a solidity to your focus. In other words, it’s steady. It doesn’t get moved around easily."

~ Thanissaro Bhikkhu "Right Resolve"