I agree with Centaurus, push in to much thrust, pitch up, get wind gust adding to light weight,you are climbing for a high altitude set in MCP,forget to delete altitude restriction in FMS, FD suddenly says pitch down NOW! Snatch the thrust levers off, pickle trim down, in attempt to return to FMS altitude, trim motor moves HS quickly in flaps 15 position,not looking through FD,tired, brain fart! Went from +20 to -15 pitch, now with HS pitch in -4 degree nose down position, try to recover by only pulling on elevator, won't work. Swiss cheese model accident compounded by tired crew. Lots of "should have,could have, would have" in this accident, lets all learn something from it. The airplane was just along for the ride, nothing wrong with it....Well said AtomKraft!