If you have a trim switch at the bow make sure none of your rods come in contact with the switch. A guy I know had his rods strapped down and thought they were secure but one of them slid forward. The butt of the rod was on trim down. His boat started losing speed and plowing through the water going down the lake. He was hitting the trim up at the console but nothing happened. He shut the boat down and heard his trim motor running. As he was checking switches he realized the butt of a rod was on the bow trim switch...its possible you had this issue with trim up as your problem.
Question...was this a isolated issue or did it happen more than once. More than once would rule out my suggestion.