My sister had subdural hematoma few years ago from an accident. She received treatment on time and she was recovered. In past couple of months, she's been getting mild headache. And yesterday, she got severe one;severe to the point that she was screaming. We took her to hospital, and few hours later she went back to normal as if nothing ever happened. Doctors took some CT scans and some other tests and concluded that there is "tiny bit" of liquid build-up in injured area and assured us that there is nothing to worry about. Since it is a hospital from third world country(even though it is supposedly the best one there), I don't really trust these doctors. So I'm planning to take her to the country(probably Canada) where she can get the best treatment. What I want to know is, what are the likelihood of she getting full-blown subdural hematoma again? Is it safe for her to take long flight (about 20 hours)?