General antonyms:
* Healthy
* Well
* Strong
* Robust
* Fit
* Vigorous
* Energetic
* Alert
* Sharp
* Clear-headed
Antonyms related to nausea:
* Calm
* Steady
* Composed
* Settled
* Stable
* Comfortable
* Refreshed
* Relieved
The best antonym depends on the context of how "queasy" is being used.