Is there a kind of hyper thyroidism that resolves without treatment ?

Yes: Dequervain's thyroiditis can make you hyperthyroid for a few days or weeks then self-cure. Another cause is eating beef into which the animal's thyroid was accidentaly placed by the butcher.

Dr Kern agreed

Subacute thyroiditis: Subacute thyroiditis generally resolves on its own within a few weeks. Also postpartum thyroiditis generally resolves within a few weeks. So, in most patients, after the hyperthyroid phase resolves, they become euthyroid but in some patients there can be transient hypothyroid phase. In a small percentage, the hypothyroidism may persist.