Normally, I would've just tried to hide my erection by pulling my pants back up and pretending to do something else, preferably the least suspicious possible, but not then.
As I was nearing the end of my masturbatory session and couldn't hold it back anymore, I closed my eyes and let myself overwhelm to the orgasm just at the same moment she opened that damned door. I knew I should've locked it, but I believed nobody would've ever bothered entering without asking beforehand.
Thus, being unable to see anything for all the time I enjoyed the, let's say, "warm feeling", I couldn't have noticed she was here since the beginning.
So, yeah, my mother saw me ejaculating till the last drop of semen, and in the lewdest way possible, even.
It was only when I was finally done and did a swift peek to see if I had done any mess on the floor, that I realized her presence.
My heart went right down my stomach at her sight: she was just standing there, staring at me with dismay, then left the room without saying anything. I'm not lying if I admit that, then as now, I just wanted to die due to the huge embarrassment that followed.
About a day has passed since the incident, and she hasn't spoke a word to me yet. She hasn't made it evident, but I strongly sense that the good old days have abruptly come to an end for me.