I went through a really bad couple of weeks after my thyroid finally died and before they started me on synthroid. I could literally barely stay awake, and missed nearly two full weeks of work due to the exhaustion. Once I started synthroid I am feeling a lot better than that (ie barely alive), but am still tired and draggy. I will be going in for blood tests and dosage adjustments for a while. They told me it might take up to a full year before I feel completely better.
I am hoping it will not take anything close to a year, though. 