I have recently began to have weak legs after I go upstairs. My legs feel like I've worked out for a long time afterwards, I become out of breath a little bit for a short period immediatley after and my heart beats fast. As well, my arms feel the same way when doing small tasks like washing my hair, brushing my teeth......I went to a neurologist who plans to do a muscle/nerve test but he said that I am probably just tired. I feel worried becasue I've never had this problem before and I don't understand how just being tired would cause this. Should I take his word for it or should I see my regular doctor about this?