Plummet and plunge mean to fall from consirable height. It can be straight down. If you see the newspapers, cars and/or buses alway 'plunge' into ravines and over cliffs. If you tumble, you can fall from a small height, even fall down from a standing position - in addition to falling, however, you also are turned around or flipped over. Your body will be spun or turned around by the fall. If you were at the top of a small hill and fell down, you would probably turn over and over going down the hill. You would tumble down the hill. I have no idea what 'slumt' means. Did you intend to use 'slam', meaning to hit hard?

maybe slump? That would mean a heavy but gentle fall. You slump into a chair at the end of a long day. Or a bag of potatoes would slump sideways in the back of the car.