Medical reasons why kids throw tantrums

Tantrums may happen when kids are tired, hungry, or uncomfortable; or because they can't get something (for example, an object or a parent) to do what they want. Learning to deal with frustration is a skill that children gain over time.

There's no such thing as "medical reasons" but more of an temper problem. Kids throw tantrums because of the anger they have over what-ever-foolish thing, but they are learning the process of dealing with anger. It's just like being mad at someone. You just have to let all the rage out to make yourself feel better. And that's fine.