car shakes on 1991 BMW 535i

The car just started shaking like it's kinds floating on the road?

Asked by for the 1991 BMW 535i
Check the rear shocks, if it has large spherical black units attached to the shocks, they commonly fail internally and require replacing. You are able to replace it with a new NORMAL shock without the round unit, should be better but you need to buy a shock and spring.
Also check the bushes