Not just a figure of speech:
Sex can trigger transient global amnesia, as can other physically strenuous activities. People in their 50s and 60s are the most likely to experience an episode, but strangely, most people with transient global amnesia have it only once. In most cases, the amnesia is anterograde, meaning people have trouble forming new memories. Sometimes, people also experience transient retrograde amnesia, forgetting some portion of their previous memories. In the case of the 54-year-old woman at the Washington, D.C., hospital, the last day was a fog, and she had been forgetful and confused since having sex. … In one case reported in 1964, a man lost his memory the moment he orgasmed, causing him to exclaim, "Where am I? What's happened?"
The Dish 