erparamedic:...
Valsalva is used in emergency medicine to slow a racing heart... otherwise known as SVT (Supraventricular Tachycardia). If you bear down too long, you are going to drastically reduce the rate at which your heart beats, and *could* potentially cause one to pass out. Wikipedia breaks down the physiology of this...
Excellent advice, and too often ignored!!!
I had this very issue early on, with my first few deeper dives (>60ffw). Experienced a bit of vertigo, until I got it into my head that when doing the Valsalva, it's quantity, not quality! Finally learned to keep it easy and often...
Btw, I do the crackling-ear boogie as well, with one ear feeling a bit 'muffled' after a series of dives... Seems to be nothing but swimmer's ear... (for me, anyway...)