eye movement during meditation

During my past several meditation sessions, which have been getting a little longer (approx 20 minutes now), I have noticed that my eyes twitch and move involuntarily -- it feels similar to the eye movements you can see when people are in REM sleep. As far as my meditation is concerned, it feels very distracting -- it typically occurs when I feel like I'm on the precipice of deeper concentration, but it results in so much motion and tension that it typically breaks my concentration. Has anyone else encountered this before? After googling around, I found one meditator explain that this was a sign of slipping into "trance," not of deeper concentration. Is that a thing? Any thoughts on remedies? Thanks!