Surprise Cum during massage

So I've been in my new Rigid Chastity Custom Cage for a week now. Through work I had a real sore back and needed a massage. I usually get a 1.5 hour sports massage which is very hard and they mostly use their elbows so it's not a pleasant massage but it really helps fix me.
As discussed with my Wife, once the new cage came I wouldn't ask for it to be removed for anything except my sport. So after booking the massage I asked her if she wanted me to wear it or would she take it off. She said wouldn't it be uncomfortable to lie on my stomach for that long with the cage on and I replied no that wouldn't bother me. So she said well leave it on then, I asked if it bothered her that someone else would likely see the cage and she said no.
I was very nervous but I did ask for this so I had to suck it up and go in my cage.
When I got there I stripped naked like usual and lay down with a towel over me. The massage lady definitely noticed as when she worked my legs she didn't tuck the towel down between my legs to cover my penis like she normally would so I know she was intentionally having a good look.
This next part was very embarrassing. Out of nowhere while she was massaging my other leg I just cummed. I quickly reached down and caught it all. I had to ask for tissues to clean it all up and there was a lot!!!! she just waited in the same room behind me while I cleaned up my mess. I lay back down and apologized and she said it's okay and continued.
So not only was this my first time being exposed to a stranger but also the first time I've ever cummed without direct stimulation since puberty. She was amazingly professional about it all but I felt so terrible.
My Wife and I are very Vanilla and she's only tolerating the cage because she knows how much better I am in every way when I'm wearing it but thats where it ends.
So when I told her what happened she wasn't sure how to react. I just apologised as much as possible and explained that it might be best if I cum within a few days of any future massages as 7 days was too much for me to handle.

Has this ever happened to anywhere else where you just cum with no clue it's about to happen.