The adjective indisposed is a slightly formal way to describe someone who's feeling sick. You might call your boss to tell her that you can't make it to work because you're indisposed.
When you're a bit under the weather, you're indisposed, particularly if you're ill enough to stay in bed and miss work or school. Another meaning of indisposed is unwilling — you're able to do something but refuse to do it. You might say, "I'm indisposed to visit my cousin because she's always so mean to me." Around 1400, it meant "not prepared," and by the mid-fifteenth century, "deceased" or "dead." The Late Latin root word is indispositus, "without order or confused."