When I first started doing yoga, I started feeling funny things in my body that some yoga teachers couldn't explain to me. I went to a doctor; he did some very basic tests and determined I had no postural hypertension, carpal tunnel syndrome, or obvious heart problems. He said yoga puts people's body in weird positions, so sometimes these weird things happen. If I keep practicing, the symptoms might go away. If they don't, then I should stop practicing yoga. That last phrase was kind of unsatisfying. I looked at him quizzically and asked, "Really? I started yoga for health reasons and you're telling me to quit yoga if the symptoms don't go away?" He said, "Why yes! If you decide to go sky diving and find out it hurts your back, wouldn't the best and most obvious action be to stop sky diving?" Then he promptly kicked me out of the room with an annoyed look on his face. Hmm, if sky diving gave me backaches, I would definitely try to figure out why, because sky diving is not an activity known for causing backaches, just like yoga is not known for being a health harming activity, besides physical strains caused by doing the asanas improperly or forcing the body into advanced asanas before it is ready for them, but that's not why I went to see the doctor. So I decided very early on to document these funny feelings because I wanted to figure out the causes of these strange sensations, if and when they will go away, and/or if there are remedies for these symptoms.
Here are the list of "funny feelings" I get from yoga:
1: I would get dizzy from continuous deep breathing.
One teacher said it was because my body wasn't used to breathing so deeply and was going into shock. This is probably true. After 1.5 years of practicing, I actually can't proudly tell you I have significantly improved my breathing overall. I can however tell you I am now capable of noticing how poorly I breath outside of yoga class. I remember going to a voice lesson a couple years ago (before I started yoga) and the teacher told me to observe my breath, and I couldn't do it without stopping breathing. Observing = "consciously taking over control of breathing" at the time. Now I can somewhat observe it while it does its thing and my breathing is pretty shallow and choppy if I don't consciously deepen my breaths. And you can only be conscious of your breaths for so long before your mind wanders off to something else again.
2: At the end of class, during cool down and before savasana, when my teacher would make us sit, meditate and observe our bodies (this was not an Ashtanga class), I would be freaked out that my chest, or my mouth, or a foot, or part of my face would go numb and then feel pins and needles. This is probably related to the nervous system not used to deep breathing (but how would I know when I first started?)
3. I would get dizzy and have brief black outs when getting up from standing forward folds.
My teacher told me to breath deeper, same advice that Sharath gave to Claudia ("and drink more water"). Someone else told me to engage my leg muscles more because too much blood or too little blood in the head both can cause dizziness.
4. After savasana, sometimes my legs would still be shaking as I walked from the classroom to the change room. Recently my teacher told me it was probably because the savasana wasn't long enough and my nervous system hasn't fully recovered yet. This is all very speculative and unscientific but I have no idea who if anyone does research on all these phenomena I mentioned and because it's not health threatening, I doubt researchers would get funding to study them.
When I first documented these things my intention was that they would go away, and then my practice would feel awesome and look beautiful and I would live happily ever after. Or I would get bored of yoga and move onto something else. Unexpectedly, because yoga teachers keeps asking us to be internally aware of our bodies, I have become more and more sensitive to body sensations, so even though I don't black out in class any more, I now sense a million other small aches and weirdness in m body both on and off the mat. The most noticeable observation is that my breathing sucks. I've gotten to the point when I can maintain steady long breathing for about 2 poses + vinyasas, then my attention goes elsewhere until I happen to hear my teacher remind us to focus on our breath (which he probably says every 2 minutes). This tends to happen during sun salutations, janu sirsasanas, marichiyasanas, and first 2 of the final 3 closing poses (definitely not during utpluthih). Everything else I don't remember being able to breath smoothly for long. Off the mat I can now often catch myself holding my breath, or feeling anxious, which happens so much more frequently than I realized before I started doing yoga.
I guess the benefit of yoga is to have the ability to do a mental body scan often during the day, and whenever I feel anxious, to catch myself and start breathing deeply. Also, if I can notice body strains when it happens (e.g. poor posture sitting in front of the computer), I can correct myself before it becomes a big enough problem that I need to go see the doctor.
As for breathing, believe it or not I still feel funny when I breath deeply through the nose (oh I used to mouth breath a lot). Maybe a couple more years of yoga and it'll start to feel more normal?