If it was a warm sunny day and the ground was cool, then you were flying in a thermal lift bubble of air. That was a dream situation for any sailplane pilot; but for a beginner with a light plane without elevator, it can be a scary situation. Just try to keep the nose into the wind with throttle off and turn back toward yourself once you regain steady flight. Being so light, they are hard to control in such thermals. The correct amount of turn control input will come with time.