Orthostatic hypotension is not a diagnosis, it is just a descrition that you rblood pressure drops when you change position. There are many causes of Orthostatic hypotension of which autonomic disorders are one set. Other problems like dehydration or heart failure can also cause 'orthostatic hypotension' for obvious reasons.
Primary autonomic failure or an isolated problem with the autonomic nerves that supply the heart and blood vessels and coordinate blood pressure responses is quite rare, but it can be affected in some more common disorders like diabetes mellitus, amyloid, guillan barre syndrome, multisystem atrophy - as you can see a wide range of disorders. Your doctor or neurologist should be able to narrow down th elist, perhaps helped by some tests of the autonomic system such as the valsalva response, heart variation to breathing, tilt table testing, some sweat testing, pupillometry etc.
These test can be done at an autonomic lab such as the one at the Cleveland Clinic Autonomic Laboratory/Center.
Low blood pressure and HR can be normal in athletes.
Low heart rate can be a sign of relative hypothroidism.
Good luck
You can get some good info at this site and there is a discussion group, too.
http://www.ndrf.org/