The answer, at least in my case, is "Yes" I can actually manifest my symptoms by thinking about them.
I am a heart worrier and if I sat here, perfectly calm with no symptoms but let my mind wander and start thinking about a heart attack, my pulse would start to increase which would kick in my anxiety so my chest would tighten, I'd then go into a panic attack and my heart rate would go way up and then my panic attack would completely take over and in about 15 minutes I would have all the symptoms of a heart attack. I've had this happen on so many occasions that I can't even begin to count; lately - last 6 months or so - I'm in a good place and have learned to keep the thoughts away and things have drastically improved. I consider myself fortunate in this.
Thinking about anything will lead you to notice things you normally wouldn't. You thought about your wrist and now notice it seems heavy - I've spent so much time thinking about my heart, I can tell how fast or slow my pulse is without actually having to take my pulse - we can train our brains to notice or ignore all sorts of stuff.
Pick a body part to which you normally give no consideration whatsoever - lets say your ears - and really think about them. How do they feel when you touch them, what do you hear when there is no noise around, how do they feel when you're not touching them, etc. It will take a while but you'll soon find yourself really in tune with your ears (in tune with your ears - great pun lol). The point is, that is a big part of health anxiety, a hyper-awareness of certain body parts. We notice them because we worry about them and we worry about them because we notice them and the circle just keeps going.