What is the definition of a mental disability and what is the limitation period for a plaintiff to pursue a cause of action?

Counsel for the plaintiff has urged upon me the broad definition of mental disability in Kirby v. Leather, [1965] 2 Q.B. 367, where Lord Denning held that an inability to manage one's affairs in respect of the cause of action would be a sufficient disability to prevent the limitation period from running. In that case he was dealing with a situation where shock and memory loss over a relatively short period of time had rendered the plaintiff "not capable of instructing a solicitor properly. … not capable of exercising any reasonable judgment upon a possible settlement". In the case at bar however we find only an emotional block which made pursuit of the legal claim distasteful to the plaintiff.