What does "I'll be sectioned" mean in Britain?

Yes - it's like the US 'I'll be committed.'

"In the United Kingdom, the process known in the United States as 'involuntary commitment' is informally known as 'sectioning', after the various sections of the Mental Health Act 1983 (covering England and Wales), the Mental Health (Northern Ireland) Order 1986 and the Mental Health (Care and Treatment) (Scotland) Act 2003 that provide its legal basis."

http://en.wikipedia.org/wiki/Sectioned#United_King...

"Part II of the Act applies to any mentally disordered person who is not subject to the Criminal Justice System. The vast majority of persons detained in psychiatric hospitals in the United Kingdom are detained under one of the civil sections of the Act."

"These sections are implemented following an assessment of the person suspected to be suffering from a mental disorder. These assessments can be performed by various professional groups, depending upon the particular section of the Act being considered. These professional groups include ASWs, Section 12 approved doctors, other doctors, registered mental nurses (RMNs) and police officers."

"Section 2 is an assessment order and lasts up to 28 days; it cannot be renewed. It can be instituted following a "Mental Health Act assessment" by two doctors and an ASW [ Approved Social Worker]. At least one of these doctors must be a Section 12 approved doctor. The other must either have had previous acquaintance with the person under assessment, or also be a Section 12 approved doctor. This latter rule can be broken in an emergency situation where the person is not known to any available doctors and two Section 12 approved doctors cannot be found. In any case, the two doctors must not be employed by the same organisation to ensure independence. Commonly, in order to satisfy this requirement, a psychiatrist will perform a joint assessment with a general practitioner (GP). A Mental Health Act assessment can take place anywhere, but commonly occurs in a hospital, at a police station, or in a person’s home."

"If the two doctors agree that the person is suffering mental disorder, and that this is severe enough that, despite the person's refusal to go to hospital, he or she ought to be detained in hospital in the interest of the person's own health, their safety, or for the protection of others, they complete a medical recommendation form and give this to the ASW. The doctors do not have to stipulate which subcategory of mental disorder the person is suffering from. If the ASW agrees that there is no viable alternative to detaining the person in hospital, he or she will then complete an application form requesting that the hospital managers detain the person. The person will then be transported to hospital and the period of assessment begins. Treatment, such as medication, can be given against the person’s wishes under Section 2, as observation of response to treatment constitutes part of the assessment process."

http://en.wikipedia.org/wiki/Mental_Health_Act_198...