The lost thought is an affliction so truly evil as to make atheists believe in the presence of Satan. One has that horrible niggle somewhere in the recesses of the mind that - seconds earlier - a thought of startling profundity and/or importance had made itself known. Unfortunately, Lost Thought Syndrome has kicked in and said thought has been unthought.
Lost Thought Syndrome is cruel, but not entirely without mercy. Sometimes an idea can be rescued by a skilled individual. Experienced thought losers are often capable of rewinding their mental processes to a stage not long before the thought is believed to have been discovered. They can then wait, as earnest observers, for time to repeat itself and pat themselves on the back - they have successfully remembered that the reason they went downstairs was to... err...*
Songwriters are particularly fearful of the syndrome. They will go to great lengths to prevent the loss of melodies and lyrics with dictaphones, notepads, etc. Ironically, some of Lost Thought Syndrome's most devastating attacks on humanity have been the result of its own passivity (see: Ice Ice Baby, Macarena).
Being a great believer in the philosophy that "the prevention is always better than the cure", my own solution to the problem is quite simple: I try not to think at all.
* complacency may be punished by Repeat Lost Thought Syndrome