The usual warnings about soliciting medical advice from strangers on teh interwebs applies. Make and keep an appointment with your cardiologist.

I felt similarly a couple of years ago after having H1N1. Took me nearly a year afterwards before I felt like myself again. Since then, whenever I get sick, I feel that way for a while afterwards. I'm fighting a little cold right now and feeling quite sluggish, although my actual performance on the bike (seasonally adjusted) is about where it should be. In other words, I only feel sluggish. I can only wear my HR strap over about 40°F, so I don't know how that's been for the past few days.

I've never tracked how quickly my HR ramps up, because I was told that how quickly it recovers is the better indicator of cardiac health. Whether this is true or not, I haven't the foggiest, but it's easier for me to pay attention to.

That said, at 55, mine ramps up pretty quickly, and recovers impressively quickly.