Sad to hear that you had to go on a low dose of thyroxine
However you mentioned that TSH
was 8 while on 50 mcg Thyroxine. ( if the blood results are correct).
To be frank, it is difficult to conclude that that alone was the reason for seizure
. What was your sodium level when you had a seizure? And did they check a sugar level at the time of seizure.
Usually it takes 6-8 weeks for TSH levels to come back to normal after proper dosing
and by that time, you should also start to feel better.