How long before it is out of your system?? { Levoxyl}

I have been taking Levoxyl for about 20 years with no problem up until 6 months ago. I started feel very strange in my head,messes with my eyes,and then moves to my heart area where it feels like it is being tightend. You can sort of feel my heart beat heavy. I believe it is my Thyroid meds. Maybe i do not need it anymore. I am 45 and think my body is changing. (oh and it is changing alright) My doc is weaning me off my meds i have went from 0.125 to .88 and now breaking that in half and it should be around .44 I feel great when i wake in the morning but by around noon these weird feeling come on and will last the whole day unless i take a anxiety pill which sometimes helps and then not. Will it be a long time before this stuff comes out of my system. I hope this is the problem and nothing else. I had my heart checked out and it is fine so they say. I would love to hear from someone if they have any input.. Thanks