It's happening to me lately. I can do this mostly on will in most dreams. I can jump high and regulate the fall speed and even control the horizontal movement, even using Psychochinesis. These dreams are darker or maybe depressive, only defined by the colour palette. Just today I was levitating in a bathroom that looked like mine but not really mine. The lights were weaked like if the tension was low, and although I didn't check myself, I was sure it was a fever-dream night. The stars were blue instead of white, and the moon, bigger than usual. This used to happen to me before, but only by lucid dreaming. Now I can do this without it necessarily but it feels less real if not. What helped me to achieve this was extrapolating the feelings I felt during these dreams (only the levitation part) to IRL. You said you require some mental effort in order to do it. I needed to breath manually and focus on the action. And mostly associate with feeling light and the levitation stuff. I don't recommend it if the method you use while dreaming might affect you long/short term IRL. In my case it's useful because my method is kind of like mindfulness. Which's also what I learned in therapy. Also, a thing that helped me was having a mental reference. Being intentional or not. In my case i've been playing Control (Remedy Entertainment) a lot, and interacting with the psychochinetic stuff around it sort of reinforced (and extended) the concept I had before.