If it's no problem for you to lay flat, a simple measure you could try to raise your blood pressure is to sleep without a pillow for a while as it tends to reset the baroreceptors.
Tomato juice is said to aid in raising blood pressure, because of its salt content I think, so you could substitute that for part of your daily fluid intake.
The hydrotherapy suggestion is interesting. It is generally suggested to finish off with a cold shower in hydrotherapy, coincidently, this is a way to increase glutathione big time so perhaps supplementing that would be beneficial too.
http://www.cold-showers.com/increase-glutathione-levels/
There is another manual therapy involving alternation of vasodilation and vasoconstriction that you can do at home which might be able to raise b p called Ischemic preconditioning or Ischemic postconditioning.
To do this needs a manual b p machine and involves inflating and deflating the blood pressure cuff, which can be around the upper arm or upper thigh, to no more than 50 mm Hg above normal systolic, for 3 repetitions of five minutes on, five minutes off. Ischemic pre or postconditioning has been proven to be safe as well as being able to condition other muscle prone to ischemic insult remote from the cuff site, i.e. skeletal muscle. Done after exertion, this could be a preventative for PEM also.
http://circ.ahajournals.org/content/112/14/2085.full
http://discovery.ucl.ac.uk/1347963
http://jn.physiology.org/content/early/2015/03/27/jn.01028.2014
http://circres.ahajournals.org/content/88/8/802.full.pdf
I can't find anything conclusive to say this will raise b p but this stimulates the same pathway response as for nicorandil (and some of the other potassium channel openers, ie diazoxide, cromakalim, pinacidil) and the organic nitrates (GTN, isosorbide etc), that is opening ATP sensitive potassium channels generally, but mitochondrial KATP channel particularly. I think this is the mechanism that raises my b p using nicorandil, the opposite of medical opinion that it will lower the b p. This is basically the drug effect without actually using the actual drug.
Further benefit might be gained from improving muscle function as dysfunction in the KATP channel is prevalent in skeletal muscles suffering from fatigue. This was what I meant to imply when I first suggested nicorandil as a possible benefit in treating ME/CFS. If that can be done without drugs, better still.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3125986/