Morgan Taylor:
Whenever I enter any of the jhanas, my eyes feel like they're rolling up (even if they're not), which is accompanied by painful strain in the eyes and forehead--especially right where the "third eye" is, perhaps not coincidentally enough. I've tried to make that area relax, but whenever I do, it lessens the intensity of the jhana. >:-(
This is a very normal occurrence once one's practice reaches a certain stage, and many yogis have experienced this same sensation/experience.

It generally signals (as in
nimitta=sign) a higher level of mental concentration. Relax and don't get your knickers in a bunch. Just use it as a sensation that lets you know that concentration is peaking. And then
use that peaking concentration to examine an insight object (or subject as the case may be).
Morgan Taylor:
Has this happened to anyone else? If I just keep working at relaxing, will it go away?
Happens to me all the time. I wouldn't be too concerned about it. Just treat it as a sign (
nimitta) of greater concentration. If you will incline the mind toward an object for insight, you may be amazed at what happens with regard to the clarity of insight that develops. But just remember: you have to put the mind in the examination/evaluation mode for the insight to arise. If you're just sitting there with nothing on your mind, nothing is going to happen in terms of insight.