If you are forgetful, you often let things slip: names, keys, why you walked into a room. It is a soft everyday word, kinder than careless. People use it about themselves with a small smile (“I’m so forgetful today”), and they also use it for a stretch of time, not only for a type of person. It does not, by itself, mean a serious illness; when doctors talk about a medical problem they usually reach for other words. You can be forgetful about small things and still be careful about big ones. The feeling is “it keeps falling out of my mind,” not “I do not care.”