Weird "bobbing" sensation?

Hi everyone! So, last night I was was asleep. Then, I woke up (a few minutes after I fell asleep, I don't know. It was hard to tell) to a weird bobbling sensation. Or it was more jerky. Like my whole body felt like it was moving up and down very quickly in small movements. At first I thought it might have been a little earthquake, but nothing else was moving. So I stood up from bed and it still happened. Then, I got back in and lay down again. About 5 seconds after I lay down, it stopped and everything went back to normal. Keep in mind this only lasted about 20-35 seconds. . . not very long! Does anyone have have idea as to what this is? Should I be worried? Thank you so much!