How do you say rolling's one's eyes or describe an eye roll in this situation?

How would you describe this situation:

Rolling one's eyes due to orgasm.

I checked most English dictionaries but most definitions are negative, e.g. due to frustration.

"X's eyes rolled back (in his/her head)".

It's true that the expression "X rolled his/her eyes" is often associated with frustration or sarcasm.

A more neutral way of describing this expression is to say that "X's eyes rolled back", or "X's eyes rolled back in his/her head". This may refer to someone who is falling unconscious for whatever reason (e.g. it seems to show up fairly often in descriptions of "demonic possession"-type scenarios), but it's also used in erotic literature to describe the situation that you specified:

• Her head and eyes rolled back, and she lost focus as the exquisite spasms erupted from her core and spread outward.

  (p. 196, My Way Back to You, by Pamela Hearon, 2015)

• Her eyes rolled back in her head as he watched her climax, and a low moan escaped her throat.

  (p. 566, Dangerous Trust, by Cynthia Monet, 2009)