You might feel various sensations when your prostate is being stimulated
You might for a moment feel like you have to go pee pee even though you probably dont have to in reality. The urethra and prostate are intimately connected and so when the prostate feels pressure it might mistake it for the bladder being full. This sensation should pass.
The urge to orgasm with the pressure of prostate.
Discomfort - when new to prostate stimulation, this can be normal alongside some tenderness. As the backdoor has never been entered and the prostate has never been touched before, it may take some time for some men to get used to. Its good to do massage very softly and gently and try again next time.
Pleasure - of various intensity! From pure enjoyment to mega enjoyment to emotional release and euphoria like state.
Prostate pleasure is different from penile one. Relax into the different sensations and let it take you to a new tapestry of pleasure