Generally not. Hypothyroidism, if treated properly, shouldn't cause any problems. If you suspect hypothyroidism, see your pcp. If you have it, take your medicines as prescribed and keep routine follow up appointments for follow up lab work. Stroke is basically not problem with this disease, and would only be possible in severe and untreated hypothyroidism. Best wishes.
Very unlikely. The only possible connection I can see would be if your cholesterol/triglycerides were so high due to low thyroid that arteries to your brain got clogged up or that your blood pressure got so low from associated endocrine problems (such as adrenal insufficiency often accompanying severe thyroid problems) that your brain lacked adequate blood flow.