I've only played it briefly, but what you're talking about is likely stalling. Stalling isn't modeled very accurately in the game and is pretty forgiving. When your airspeed is too slow in an aircraft you don't have nearly as much control, things become sluggish relatively quickly as air speed drops. Part of that is also the nose having a tendency to drop.
throttle up or flaps? It's planes not helocopters, you need a minumum speed to stay airborne. If this is happening when your clawing for altitude to get to the bombers you can try flaps when you get the airspeed warning, stabilize to level flight, gain some speed and raise flaps, climb again when you have higher speed. Chasing high altitude bombers is hard for a lot of planes. Best with ME 109's and P-39s and their like.