Could these symptoms be related? joint pain/ inflammation, fatigue, postural hypotension, dry mouth, poor memory/'fog', arm/hand twitches, clumsiness

Team approach: The symptoms you described is a serious medical condition and needs to be addressed as a PCP-led team approach. Each member (specialist) of the team plays a critical role in delivering proper diagnosis and treatment. Comorbid conditions do not go away on their own they need to be addressed together and separately.

Possibly: It is possible that you may have one single condition, although it would seem more likely to be a number of conditions that may be contributing. There are a number of inflammatory arthropathies, lupus, for example, that can cause joint complaints but also a variety of systemic manifestations in their more advanced state. Consider being seen.

Need to see doctor: to sort out the symptoms. You may have more than 1 problem and need a doctor to help sort it out.