There are no known causes for Idiopathic Intracranial Hypertension, hence the word 'idiopathic' which simply means a condition or disease that arises with no known cause. There is also Secondary Intracranial Hypertension which means that the cause for pressure increase in the skull is a form of head trauma. It mostly occurs in patients who have been in car accidents etc.
There is a clear link to IIH and being overweight, however this is NOT a cause. It means that IIH usually occurs when women are of child-bearing age and are overweight. There are some cases where a person is of a healthy weight and still has IIH. On the other hand, there are some people who find losing weight relieves their symptoms and they often go into remission but each person and how they react to this condition is different. What may work for someone else, may not work for you.
There are things that can spontaneously and oddly 'set' this condition off. As a person with IIH myself, I find that things like stress, the weather, humidity and things like bending over can cause a headache/migraine. With me, bending over to tie my shoe laces for example, makes me feel like my head is underwater and I usually have an off balance weird moment which is hard to explain.
So there are no known causes for this condition unfortunately but our bodies tell us what they like and what they don't like. There are a range of treatments to losing weight, to medication, to shunts and stents. There is no cure so we have to figure it out. Our bodies give us signals, we just have to listen.