I am a pretty big hypocondriac (Anxiety has always been a thing but a recent family scare set me off on this)
I have been explained by my psychologist this fact:
The human body has lots going on all the time. Lots of aches, pains, noises, feelings. Its much easier to notice them if you think about them. This is a fact. Patients when asked to think about a certain area come up with pains there easier.
I do the same thing. Of course you should probably see a doctor if this "dizziness" is causing you to fall over or noticeably stumble or your heart problems are caused by pain.
Getting a FULL physical is probably a good idea for you as well. this set off my hypochondria a bit because I feared the worst.
But after its done you should at least have a good idea that you aren't dying (although it didn't convince me totally
I'll give a personal example. I have been twitching a bit lately due to being horribly on edge for a few months. If I don't think about it I barely notice it. When I think about it I notice it alot.
The mind is very powerful. Truthfully it sounds very much like my anxiety. One of my fears has been getting MS or ALS (common fears with hypochondriacs) or brain tumors. So sometimes I monitor things that would be symptoms of those things like constant clumsiness etc... I notice that if I think about these symptoms while typing or playing my guitar I screw up more then If I'm not thinking about them.
Anyways go to a doctor if you believe its serious but as a hypochondriac myself I doubt it is serious.