In the mid-1990s, after leaving Whose Line Is It Anyway?, Slattery suffered what he described as a "mid-life crisis" – triggered by excessive drinking and cocaine use (spending up to £4,000 per week on the drug) – culminating in 1996 with a six-month period as a recluse, during which he did not answer his door or telephone, "or open bills, or wash... I just sat". Eventually, one of his friends broke down the door of his flat and persuaded him to go to hospital. He was diagnosed as suffering from bipolar disorder. He discussed this period and his subsequent living with the disorder in a documentary made by Stephen Fry, The Secret Life of the Manic Depressive, in 2006; Slattery claimed that he spent time living in a warehouse and "throwing [his] furniture into the Thames".