Interesting issue. Males clearly have wet dreams with evidence that something occurred - a spot on the sheet. We women tend to not have sexual dreams all the way to orgasm. Both men and women usually awaken for the orgasm. We women will often awaken in an aroused state and have the option finishing ourselves. I usually do.
The completely spontaneous orgasm in wome is much less frequent but not unknown. At some level you were haing a sexual dream or hidden fantasy that you were not aware of in that nether worl between awake and asleep. I have awakened on the verge of orgasm but not with an actual orgasm. I almost envy you!
Men have a physiological reason for wet dreams. The excess of semen and sperm that builds up in the male system is usually reabsobed into the body. When there is too much for reabsorbing, a spontaneous ejaculation occurs. We women have no such physiological necessity, so our spontaneous release is a result of psychological factors. Some deep memories whether consciously or not cause us to experience orgasm. Romantic thoughts trigger mine rather overtly sexual thoughts.
This is clearly a long time thing. In the ancients, spontaneous orgasm in women was blamed on an "incubus" - a male spirit that lurked and had intercourse with sleeping women. He/it disappeared as consciousness returned. The analagous cause of men's wet dreams was a "succubus." This was a way to attribute sexual response to an outside cause ("creature"
so that no one had to admit to being sexually aroused spontaneously.
Your "condition" is quite normal and longstanding. Enjoy!