Asp, you are fortunate that you have symptoms in time to catch it - and you recognize what it is enough to say something. Some do, but most don't. Trying to push through it never works, so you are wise to notify your Top and have them get you flat.

Unfortunately, most don't have early symptoms or if they don't, they don't recognize them for what they are - a precursor to blackness. On occasion, I've touched a sub and felt that cold sweat or looked into his eyes and saw that blank stare and knew to get him vertical, but it's rare to get the indications in time to act.

As far as that blood pressure drop due to My entering the room, there's not much that can be done about that - except may condition training . . .