Name for symptom? Ground suddenly moves underneath me

Is there a name for this symptom? Sometimes (once every day or two the last few weeks) I have the feeling that the floor has suddenly moved underneath me. Like, it will feel like the ground has suddenly dropped down underneath one foot, or that the ground has suddenly shifted sideways, or like if there was some big jolt that knocked me off balance. It just happens as one single "movement" not like things are constantly moving, not like things are spinning, so I don't think its vertigo. I tried looking it up but all the results were about vertigo or anxiety, but I don't feel anxious or anything at the time; I'm just standing, walking, or having a normal conversation.

Its weird because its not the whole "environment" that is affected - I don't feel like I've suddenly dropped (like that feeling you get sometimes when falling asleep) or that the room is moving. It'll often specifically be the sensation that the ground under my right foot but not my left foot has collapsed, for example. Making it seem like its more a problem with perception in my feet. But I'm not sure.

Anyway, just thought I'd ask and see if this had a name or anything.