This is so confusing

My husband (74) was having dizziness & balance issues, brain fog, and crushing fatigue and then after quite some time, a mild tremor in his fingers when he held his arm out, so his doctor sent him to a movement disorders neurologist. They seem to think it's Parkinsons but his a-synuclein test was negative (he didn't have a DaT scan), his tremor is not a resting tremor that is typical of PD. And I don't think the fatigue is typical? That was his first symptom. He'll sleep 12 hours at night and take 1-2 one hour+ naps a day! Even putting him on Amantadine didn't help with the fatigue. He wonders if he could have Long Covid. Or maybe there are multiple issues going on. He does have sleep apnea but is being treated for that.