vacillating

Vacillating between silly and serious, the talk with Ansari is interrupted several times with giggling—most of it his own.

Vacillating and unintelligent, his actions were all guided by his mistress, Mme Bonnemain.

I suppose it is characteristic of people who tic to be fickle and vacillating.

For her restless and vacillating husband—he was this in her eyes as she mused—she had discovered nothing new in six years.