Thanks for the replies.
Earthdeva, I also felt it as a gushing through the crown that filled my entire body. For me, the climax only lasts for 10-20s maybe. Until yesterday I had always done it laying down before bed at night, and so after enjoying the post-climax stillness I just decided to go to sleep.
However, yesterday I did it during the evening and was awake for many hours afterward. For the next hour or so, my head felt light and slightly euphoric, like a positive headache.
Steven, some other details that might help if you are going to try it. My first time I was laying down alone in bed, hands on bare chest, with someone else in the next room who didn't know what I was trying to do. This gave me the space to let my body's inhibitions loose, while knowing I could call out to someone if I felt overwhelmed, while being under no pressure to perform.
I think it helped that I thought something important was definitely going to happen. Truthfully, I anticipated I might levitate or be contacted and I was fearful of this - and that didn't happen. Overall though, I think it helps to be sure that something amazing is going to happen, and that you have the power to bring it on.
Good luck and keep me posted!