The diagnostic criteria for POTS include both an increase in heart rate of at least 30 bpm or to at least 120 bpm overall from supine to standing (or upright tilt in a head up tilt table test) as well as symptoms such as lightheadedness, dizziness, fatigue, shortness of breath, presyncope, and/or syncope. That's not an exhaustive list of symptoms, and a patient does not need to have all symptoms to meet the diagnosis.
Some patients with POTS have an increase in blood pressure upon upright tilt or standing. Within this group, some will have an initial increase in blood pressure but after some period of time may experience a sudden drop in blood pressure such as in neurocardiogenic syncope. Others will not have such a drop in blood pressure and do not experience syncope.
Some patients with POTS have no appreciable change in blood pressure upon standing or upright tilt.
Some patients with POTS initially have no change in blood pressure upon standing or upright tilt, but after some period of time may have a decrease in blood pressure and may ultimately experience neurocardiogenic syncope.
Some patients with POTS do have a drop in systolic and/or diastolic blood pressure upon upright tilt or standing, which may remain consistent or persist in falling to the point of syncope.
Definitions vary somewhat, but generally speaking "orthostatic hypotension" is defined as a drop in systolic blood pressure of at least 20 mmHg or a drop in diastolic of at least 10 mmHg (which is sustained, not momentary). So looking at your numbers, your diastolic drop is pretty significant, thus the diagnosis of orthostatic hypotension.
Diagnostic labels in dysautonomia are far from standardized. Some doctors stick with the general label "dysautonomia," while at the other extreme other doctors diagnose every aspect of dysautonomia present in a particular case. And of course there are degrees in between, and many forms of dysautonomia have multiple equivalent terms, or terms that some doctors use interchangeably while others use them for shades of meaning.
All that being said, if you think you may have POTS in addition to OH, and your doctor has not addressed this with you, it can't hurt to ask. It may or may not change your doctor's treatment plan for you. Do you have palpitations, heat intolerance, exercise intolerance, fatigue, shortness of breath, presyncope/syncope, nausea, brain fog, tremulousness, or other POTS symptoms? Since your heart rate increase is right on the borderline for the diagnosis of POTS, it may be helpful to discuss these with your doctor as well. If you haven't read Dr. Grubb's 2008 POTS article, I recommend you take a look at that, which you can find here:
http://www.medhelp.org/health_pages/Neurological-Disorders/Further-Reading-on-Dysautonomia/show/696?cid=196
If you really want an in-depth understanding of syncope, orthostatic intolerance, POTS, and pretty much everything in between, you may want to spring for his book which is also linked to on that same page. (I linked to the amazon.com listing; you may want to try to find it elsewhere or ask your local library to secure a copy through inter-library loan.)
Feel free to let me know if you still want more clarification, and just let me know where i need to be more clear!