It is not possible to completely answer this question without seeing your thyroid function testing most specifically your TSH levels. That is why it is important that you continue to follow-up with your endocrinologist
. With that said, generally speaking, missing one dose of your low-dose levothyroxin does not seem to be the cause of your symptoms returning. There are a couple of reasons for this. First, levothyroxin always lasts a long time in the blood. We always tell somebody that if they miss one dose of levothyroxine, they should always just take 2 the next day. This never results in anybody getting too much or too little thyroid hormone. I should also point out that with your dose being so low I wonder how much your symptoms have to do with hypothyroidism in the first place. 25 µg is almost no levothyroxin at all and I have never seen anybody have resolution of symptoms due to hypothyroidism from such a low dose. You should continue to follow with your endocrinologist for this problem. He or she will monitor your TSH levels and use that to determine how much levothyroxin you need. If your TSH levels are normal and you still feel the same symptoms, then you will need to look for a different cause for these as your thyroid function might not be the only problem.