What do these phrasal verbs mean?
- You wake up and sit up.
- You wake up and sit down.
And can you include some more example to illustrate the point clearer?
Sitting down is usually from a standing position. If you sit in a chair, on the floor, or on the bed from a standing position, you sit down. Sitting up is from a lying position, or slouched position when you are sitting. When you are lying in bed, for example, and come to a sitting position, where your back is straight or is leaning on the headboard, you are sitting up. In these positions, your feet can be stretched out ahead of you on the bed, or they can fall over the edge of the bed and bent at the knees, while your buttocks are on the edge of the bed. Unless you are sleeping in a standing position, I can't imagine how you can sit down. You might wake up in your bed and then sit down on the floor or in a chair.