While walking in the mall this after about 90 minutes, I began to get tighten biceps, as if I had just, done several sets of biceps curls, and started to get light headed and from there an upset stomach. Also, just yesterday I walked on the treadmill for 60 minutes at 3 mph and lifted weights for 30 minutes with little time between reps and no problem or concerns plus felt great! I walk each day about 10,000 plus steps each day and lift 2 to 3 times per week. Further, two days ago will swimming in my pool took two laps and felt tightness in my pecs (chest), not something that ever happened! Moreover, had a headache last night while sleeping, although I get headaches often sinus headaches, not at night!