Is it ALL in my head?

I feel like I'm battling with myself over whether symptoms I'm feeling are legitimate physical symptoms that should be checked by a doctor or if they are related to anxiety. As you know, my recent trip to Mather would seem to indicate that anxiety is in play. Initially. knowing this was comforting and helped how I felt physically as well as mentally. As the weekend continued, this battle started to creep in again. On Saturday, I made the mistake of mowing both the front and back lawns rather than splitting them up over the weekend. I was very tired for the rest of the day and most of Sunday. On Monday, I worked in the morning as our marching band performed in Bohemia's Memorial Day Parade. I was outside for about 3 hours and felt pretty good marching the parade. We had some friends over for dinner and following dinner I was cleaning up and felt the need to sit down. My legs became very shaky and I got very warm and sweaty. This felt like one would feel when their blood sugar level is down. The only problem with this is that I had just had a nice dinner of grilled chicken, corn, watermelon and pasta salad. Our guests had baked cupcakes for the kids and I might have had a bite or two of Thomas's. Eventually the sweating gave way to some slight nausea and then the chills. I even had to put on a sweatshirt and cover myself with a blanket. I was very scared and wondered if this was going to land me back in the ER. I waited it out, slept a bit and eventually felt better. It would seem to me that this was not anxiety related. Is it related to my current medical condition or was it something else. Did I overdo it, by marching in the parade and then having guests over? Did this cause the problem? Do I have some other medical condition? Is there some kind of infection in my head from the surgery? This is what plays in my head during this. I slept well last night and this morning woke up with a kind of burning discomfort on my right side...feels like the lung area. Doesn't hurt more to breathe deeply, but just breathing normally I feel it. This is similar to what I'd felt last week. But of course, my mind begins to wander towards what this could possibly be and this always includes worst case scenarios. But I keep trying to tell myself, "They did a chest x-ray, and a CAT scan on my chest. If there was a problem with my lungs, wouldn't they have seen this?" It's a constant battle.
Overall, I'm getting frustrated by how long it's taking to get back to feeling good every day and performing my normal daily routines. I know it hasn't been that long, but I guess I have higher expectations for myself. I'm tired of feeling less than 100% and I want to be able to get back to normal, but my head and my body are holding me back.