"Only go as far as you can and never strain. YOGA IS *NOT* ATHLETICS!" - written on the JoS hatha yoga webpage.
You most likely change asanas pretty quickly and you force yourself into them, this is why you feel heat and you sweat, and also your heartbeat is faster.
Try doing easier asanas first and take your time to *feel* how your body stretches and the energy buzz, and also take a few seconds rest after every asana and concentrate on the buzz you feel in your whole body.
About trebles, try to clam down and be in control of your own body. YOU are the one who moves it, not vice versa, and this "control" is built in time and with every yoga session you do. With every simple yoga session try to feel what your body needs and what is its potential and exploit it healthily, never go beyond it.
If you can't do something being relaxed and you start to treble, forcing yourself into it just don't do it for now and you will eventually get back to trying it again after some time, not a big deal.
Try to see yoga as something extremely relaxing, which calms your body and opens channels in your soul. Maybe see it as a form of art? However you want to but just know that it is not stretching, and it's never forced, pushed or rushed just so you avoid these things you say you experience.
Also make it a pleasant activity! I personally listen to classical music while I do my hatha yoga sessions, you can also burn a scented candle, or whatever you like unless it's distracting you from concentrating on the energy buzz and getting the most out of it.
