Strength & stamina during sex

[dandelion5]

Prior to this recent setback I'm having, I was steadily improving and able to climax during sex. However, I notice that if I need to physically exert myself (like if I'm on top during intercourse) I feel very weak. I don't have that adrenaline surge that used to make me feel physically strong during sex. Like you know that feeling when you're getting closer to orgasm and your heart is racing, but you feel good, like you have enough endurance to do whatever you need to in order to climax? That's gone. Now I actually feel physically weaker the closer I get to climax, so it makes it difficult to keep going. I feel so out of shape. It's embarrassing. Same thing with masturbation also.

Has this been anyone else's experience?