Suddenly Felt Sensation In Chest, Light Headed And Nausea, Shortness Of Breath. What Could Be The Cause?

Question : Hi. I'm a 43 year old male. My problems seem to have begun a year ago. I was sitting in a chair, and stretched way back with my arms behind my head, and felt a sensation in my chest. Then I felt flushed and hot all over and lightheaded, and had some nausea. Went to emergency room, with symptoms coming and going. Stayed overnight, and heart enzyme and blood tests, x-rays were taken. All negative. Had a heart catheterization, and two stress tests later which were negative. No diagnosis from that event, as symptoms improved and seemed to go away, except I was later confirmed to have sleep apnea, and bradycardia, which neither one of those proved to be much of a concern, except I now use a CPAP machine every night. However, I have had symptoms return in recent months, prompting emergency room visits in various hospitals that have not lead to any further diagnosis. I have been having numbness and pressure in my left arm and left side of my neck, and intermittent XXXXXXX leg and pelvis aching that comes and goes. Along with this usually comes heaviness in my chest, and weakness and nausea. I am also fatigued a lot, but the other symptoms come and go at random. Standing and moving around occasionally helps me feel better. Laying down doesn't always help, and sitting seems to maybe aggravate it at times. Last night I felt good except for tightness in my left bicep, but after I rubbed underneath and all around my arm, the wave of nausea and discomfort around my chest came back,and I had to lay down for an hour. The worst of it often lasts for at least a half hour or so. The numbness and/or pressure in my left arm and upper chest near my shoulder seems to always be there at least slightly. About twice a month I get bad chills that last for a few minutes. I do not have shortness of breath or sweating with this. I am 6' 0" and weigh 245 lbs. I do HVAC service work consisting of short periods of stressful activity and physical exertion, followed by 15- 20 minutes of sitting while driving. I am not very active when I get home, watching TV or reading for hours. Only history of any heart problem in my family is one grandfather. Thanks very much.