[OMFG!You'reActuallySmart!]

Hypothyroidism and improper dosages of Synthroid can lead to changes in mood, irritability and stress. Although hallucinations rarely if ever happen, you can have impaired cognition, which when combined with the stress, can make it easier for you to misinterpret something as a hallucination. You begin to worry about that and combined with the stress from the medication and hypothyroidism, the idea that you are having hallucinations is strengthened.

In psychiatry, a rule of thumb is the earlier psychotic episodes including hallucinations occur, the more severe the symptoms and the harder it is to function without someone noticing something is wrong even when they cannot determine exactly what. I think it's more likely due to your improper dosage and hypothyroidism.

If I were you, I would see whether the changes in mood and anxiety decrease as the dosage is brought to where it should be. The hallucinations would likely also decrease. If they are unaffected or intensify after the mood swings and anxiety decreased, then it's time to check in with your doctor.