Here is a good link:
http://www.freediver.co.uk/finalsite/techniques/pranama/index.htm
Also there is some links in other threads.
My blood pressure decreases in 5:20:10 breathing pattern, to be exact it is the breathold part. This causes dizziness. Once I fell to the pool, when doing this kind of exercices while sitting in the edge of the pool.
Later I made some experiments with my blood pressure gauge (Omron M4).
state upper lower pulse
------------------------------
normal 131 91 61
static1 90 75 90
static2 76 63 83
Normal state means, this is with normal breathing sitting in front of a table. upper is the higher part of the blood pressure as mmHg. Pulse is beats per minute. My normal rest pulse is 56 when sitting and 48 when laying and very relaxed.
Static is measured about 20-30 secs after I have started static while sitting.
Conglusion: I don't want to do static exercises while sitting or standing, maybe pranayama. I'd rather do these exercises while laying in sofa.