Tense Muscles

Hey All,
I have been using the Helix Syn for about a year now and I love it. I have had some great sessions with it. No Super O though. Lately while using it (laying down, feet flat, knees bent) my calves tighten and get really really tense and it throws me off. I get amazing tingly feelings and sometimes great p waves but I can not seem to relax my legs. I have tried on my side and it helps my legs but does not get me even close to the feeling I get while laying on my back. IDK if any one else has had this issue before and can offer some guidance to help me loosen up my legs so I can start to get the shakes you lucky guys get. IDK if it matters but I am 25 year old. Thanks for the help!