It is an inevitable aspect of life, but it is also an unpleasant one. All of us succumb to illness during our lives, with some obviously more perilous than others. Illnesses such as flu, a cold and migraines are not necessarily dangerous, but they make us feel terrible all the less. There are illnesses which are much more hazardous to our health, and ones which can affect us for the rest of our lives. There is no need to mention these as we all know which types are the most dangerous and which can affect us the most.