Example of a shop which describes 5g as a "light dose": https://www.sirius.nl/atlantis/
Especially with the effects being temporary - can you imagine how awful it must be to regain lucidity outside of your control and then lose it again for the sake of an experiment like this? Awful experiment.
I would imagine the losing it again part is typically somewhat similar to how someone remembers a surgery under anesthesia -- they don't.
As far as ethics go, I would absolutely sign a document that gives the right for experimentation in the event I become incapacitated to some degree.