My mother went to the hospital to have fluid drained from her lungs is it comon for the drs to medically induce you in a coma?

Cases differ: it is unlikely that the only problem is just fluids on the lungs, there is more, and doctors deal with what they face at the time when they deal with a case. Your mother's condition warranted a specific measure according to the doctors' judgement at that moment, trust your doctors and their judgement they definitely want the best for your mother, wish you all the best