There is something about the sight of blood when you spit that makes all my spidey senses fire up and my intital instinct is to run in circles screaming "I'm dying! Call an ambulance, call a priest, call the shoe dept and give them my regards" I mean coughing up blood is just WRONG....but then I give myself the old "snap out of it" (a la Cher) and run down all the reasons this happens and why it's not a real big deal and that I should just keep my cool and keep an eye on it.
I wouldn't quit doing the HTS or anything else. Particularly since you are pretty sure you have a sinus infection going on. To me this seems like a time you want to be very sure to be moving that excess mucus out. And I must view a little blood in the mucus way different than everyone else? I mean while I think it's worth mentioning to the Dr. I don't think it's stop the presses interesting or certainly anything to stop your treatments over. Coughing up straight blood, or having an active bleed going is to me an entirely different thing than just blood in the mucus. And there's no mistaking one for the other, when your lungs are actively bleeding you know it.
It sounds to me like you have pretty much figured out why there's probably some blood in your sputum and yah I would tell your Dr. but like I said I wouldn't quit doing your stuff.
Sorry, this was a rambler <img src="i/expressions/face-icon-small-wink.gif" border="0">