Much of what is being described is postural hypotension. This is where your blood pressure drops dramatically when you move quickly from sitting or lying positions to standing. This is very common in the general population. Lots of different causes and lifestyle adjustments are the main treatment, along with treating underlying conditions, like dehydration and anemia.
http://www.mayoclinic.com/heal...-hypotension/DS00997You should rule out dehydration, anemia, drug effects, neurological conditions. One thing to think about if you were on long term or high dose steroids is adrenal insufficiency. Even if it has been months or longer since you last took any steroids, this should be on your radar. The adrenals can be suppressed by long term prednisone use and you could have been secreting enough generally, but now are running a bit short, especially if your daily stress levels have increased, with return to work or other things going on in your life. The effect can be subtle, but unexplained symptoms can be important to recognize. Worth exploring if everything else checks out. This effect of steroid use can last up to a year after stopping them.
http://www.nadf.us/diseases/SE...%20INSUFFICIENCY.pdfJan