So, here's what happened. I transported the keyboard because I'm staying at my Dad's home a few days, and then I temporarily placed the keyboard on it's edge, resting up against a chair, on a tile floor. Suddenly, it started slide out away from the chair, and I was too far away to stop it. When it slid out far enough that the upper side was about 16-18 inches (40-45 cm) off the floor, it then just dropped the rest of the way -- SLAM! -- and the side even bounced a few inches. It was the bottom of the keyboard the slammed into the floor. Everything looks okay -- no cracks or visible damage. And the sound seems normal, though I'm running it on batteries for the first time (I left the AC adapter at home and don't have access to it right now).
However, there is one sound that has characteristics that I did not notice before. It is the Dynamic Overdrive sound (in the guitars section of the panel voices). It is sound number 40 on the E433, likely a different number on the E443 and E453. When I hit the key softly, that sound quickly fades out, almost like a (distorted, as expected) plucked string. But when I hit the key harder, the sound lingers on for much longer. Is this normal for this sound? I never noticed this before.