Suspension?

My favourite thing about my car is the amount of money she likes to milk from me!
I have a 1.8 1998 Petrol freelander. She has been shaking in the floor at between 50-70 mph, tried the obvius first and balanced the wheels, made no difference.
Then i noticed that when i stood behind it, it is slightly lop-sided, dropping on the rear wheel. maybe only 2cm?
Any ideas as to what this could be?

Thanks.

Shock absorber failure?

Have a jump on your boot lip, see how it feels.