Today, for the second morning, I got up and did not have postural tachycardia. The key is to drink a glass of water 20 minutes before rising and to get up slowly, keeping the knees bent and slightly leaning forward.
I have also managed to walk around the house without getting tachycardia, there's a small rise in pulse going upstairs but within normal limits. As long as I keep my fluids up I feel I'm winning the battle. Going for walks is proving more of a challenge, I'm trying to keep the pulse below 110 (for a gentle amble) and this is fine for the first 5 minutes; I slow and drink water when it starts heading for 110. It can suddenly jump to 120 and I stop and cross my legs over, as I know if it sustains at 120 it will trigger fatigue. It is so unpredictable, it can be 120 and then drop to 85 on standing still and then stays at 95. There seems to be no rhyme or reason. I'm guessing variations of fluid levels alter it. Last night it suddenly shot to 150 while walking despite me not feeling any different. I'm hoping that, just like my standing pulse has improved, my walking pulse will also get better over time as my venous return improves.
Then it will be upper body I need to work on. I currently get a rise in pulse every time I raise my arms, even brushing my teeth gives a slight rise and getting dressed also triggers it, let alone doing the laundry or sitting to chop vegetables. But I figure upper body strength will be helped by Iyengar yoga and I need to practice getting back to standing poses to get the full benefit. At the moment at home when I get tachycardia I sit crossed legged on the floor and it returns to normal - I managed to play boules sitting down at the weekend