Hospitalization may be necessary for seriously ill patients, or for those who are a real danger to themselves or others. Though for some people hospitalization may be a more destructive move than not. It is easy to come dependant on the hospital and, if having been in for a while, discharge can be a huge upheaval causing much distress.
In some cases you may not have an option on whether you go into hospital. If you are unwilling to be a voluntary patient and the doctor thinks you need to be admitted, or you are wanting to discharge yourself and you are not seen well enough to leave, he can place a section on you. This means you have to be in hospital until the doctor says you can be discharged or until the section has come to an end.
Hospitalizations can be for only a matter of days, or the other extreme, years. Average psychiatric admissions are about a couple of months but it really depends on your condition.
If you feel you need to be admitted to hospital, contact your nearest psychiatric hospital and arrange to see someone from the emergency team. If you feel it's not an emergency contact your GP.