If it doesn't have a flat tire, I'd suspect that there's one or more tires with problems like severe wear or out-of-roundness due to tread separation. You might not be able to see that the tread is separated unless you could observe the tire rotating. If you were to drive slowly and it feels like you're going over a bump every time the tire turns, you may be feeling that out-of-roundness.
That was only my first idea. It gets worse from there and I don't think that the car's safe to drive until you fix this problem. Please get it checked out ASAP at a tire shop or a Toyota specialist.
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