I am newly hypo after RAI and need frequent blood tests. Last month I had several days of dizzy spells and needed to lay down before I fell down. My BP ranged from 96/56 to 104/62. TSH had gone from 0.018 to 8.2 in one month.
For me, thyroid has a big impact on my BP. 6 months ago it was 196/135 when hyper.
So I would say yes, undermedicated can cause dizziness.
thyroid dysfunction seems to cause dizziness in me
Someone else would have to answer if the thyroid itself can cause dizziness or not, but I know when I was on synthroid last (and will be again shortly) it could make me dizzy sometimes. And take a look at your drug sheet that the pharmacist gives you? It may say that dizziness could be a sign of an allergic reaction. Mine did. I had hashi's and the synthroid would throw me hyper, so I'm not sure if it was the thyroid or the medicine. I start back on synthroid tomorrow. So I'm a bit nervous having had troubles on it before, but I have no thyroid now, so I'm hoping it will be a different situation.