Hi Thomas,
"Something pulled me back" sounds to me a lot like an out-of-body dream/experience, caused by your degree of development in concentration skills. Stuff like this starts coming up in A&P territory; being able to sit for long periods is also A&P-ish. 3-D stuff may indicate 4th Jhana, like Trent said.
If you want to figure out "where you are" in order to avoid dark-nighting your way through exams, you should give the
Progress of Insight chapter in MCTB a careful read (not just that first Wiki page, but the entire chapter). The big table summary of the progress of insight, found on Daniels homepage, is also very useful.
Some random thoughts on 4th Jhana, and "samatha jhana vs vipassana jhana":
- In 4th Jhana, the difference between samatha and vipassana jhana is becoming increasingly small. With stable 3-D imagery, how hard is it to resist examining the special effects, investigating, penetrating? OTOH, it also becomes tempting to buy into the content of the special effects - i.e. to wonder whether that OOB experience or compelling vision was "really real", instead of figuring out what leads to what.
- Being able to access a Jhana, and penetrating/investigating/figuring out the Jhana are separate "steps" so to speak. They strongly tend to be accessed in sequence (though that sequence can be very quick), and penetrating the Jhanas also occurs in sequence (the progress of insight models this sequence). One crude way of understanding the relationship of these two sequences is that being able to access a jhana indicates some degree of penetration of the previous jhana. This is not a hard rule, but if you can get to 4th, this could very well indicate quite a bit of penetration of the first three - read: you might already have had more than a taste of the dark night. But maybe not. This coupling is not very dependable, just one more factor to take into consideration.
- If you are worrying about hitting the dark night at an inappropriate time, in addition to not doing insight practice (which may or may not make sense if you hit 4th, see the first point), you should really make use of a formal resolve not to make progress at this time, until you resolve to do otherwise. Formal resolves of this kind are really astonishingly effective. You can think of your powerful concentration skills as giving your formal resolve extra leverage, if you like.
I hope there's something in there that's useful. Good luck with your studies!
Cheers,
Florian