Matsuura Aya has recently revealed that she has a medical condition called endometriosis.
According to the announcement she has had this condition for a couple of years now and just recently she decided to announce it.
Basically the condition involves cells from the uterus growing outside of the uterus, producing pain in the pelvis among other things, so from what I can understand it seems that this condition is somewhat serious since it affects the area involved with reproduction resulting in a possibility of infertility (not being able to have children), and while the symptoms aren’t life threatening the condition is still of concern since it’s a fairly uncommon condition (5-10% of women have it).
I’m not a professional so I have no clear idea about the pain and treatments available but this might be at least a small reason as to why Ayaya hasn’t been performing that much in the past few years since her graduation, although it’s understandable since the main area affected by the condition is the center of the body used while dancing, which would probably be really painful to do, especially for the length of an average concert.
The condition is unfortunately not curable (the symptoms are, but only after menopause) but I wish the best of luck to Ayaya and hopefully she takes the rest she needs.