I believe they trance because they are automatically playing dead, and they become very relaxed. You can think of it as more of a psychological state then a physical one.
The reasoning behind it is, they are caught by a predator, fighting back is no good, so play dead, predator drops you, you run off;
Typically you can tell if a rabbit is very nervous during a trance; Mine are; I’ve met one bunny who loved being tranced and having his tummy rubbed. If lulla wasn’t distressed by being tranced (didnt’ run off foot flicking and stomping) then your probably fine to do it to her. I wouldn’t do it for hours but by all means a few minutes should be fine! I think stress is why you want to avoid doing it for extended periods or quite often…
If you want, go on youtube and use the keywords ‘a very unusual bunny’ there are some great videos this lady did of funny things her bunny does; including very relaxed trancing. 