The word "queasy" has uncertain etymological origins, but it likely comes from a Scandinavian source like Old Norse "Kveisa" (meaning "boil" or "bowel pain") or is influenced by Old French coisier (meaning "to hurt") and Anglo-French "queisier," which itself might stem from the same Germanic root as "kveisa".  It entered the English language around the 15th century, and referred to a feeling of nausea or unsettled stomach. 

According to the Oxford English Dictionary, the adjective "queasy" was first used in English around 1450.  Specifically, the OED's earliest evidence is from the Middle English period, in the text Practica Phisicalia, a recipe book by John of Burgundy, although some date his works to between 1338 and 1390.  The word appears in Middle English texts as "coisy," "coysy," "queisy," and "qwesye." 

Examples of using "queasy" in a sentence:  
"It made me a bit queasy, as these things tend to do,’ he said." 
"The board ride made me a little queasy." 
"She complained of a queasy stomach."
"He feels queasy about taking the test."
"She had the queasy feeling that she was being watched." 
"If public speaking makes you queasy, practice reading in front of supportive friends or family members." 
"For example, if you always eat pepperoni pizza before your cardio workouts, and you always end up feeling a bit queasy, it might be time to try a different pre-workout meal." 

Just the facts:

QUEASY Definition & Meaning - Merriam-Webster

QUEASY Synonyms: 93 Similar and Opposite Words | Merriam-Webster Thesaurus