unable to manage the onset of body shaking during sessions

i have very enjoyable aneros and a/less sessions.

i am quickly into my pleasure zone and soon feel the exquisite sensations that i am able to generate alternately between my prostate and anal sphincter.....bliss.

however , i am unable to sustain this for very long because my stomach pulls in , my body starts shaking ,my head and shoulders lift up and am left catching my breath and the sensations subside.
i quickly calm down and start again and am able to repeat this for as long as required.

i try not to over stimulate.....try to focus on deep breathing ..........i just lose control.

i would love to be able ride these fantastic sensations for a sustained period of time.
sm