omr

I have had my 04 for more than a year now.
I have an issue (since I bought it) that comes around occasionally and then corrects itself.
My dealer states this is normal, and since no fault codes show up, he says he can't find anything wrong.
Since this is the usual crap that dealers pull, I'm asking here.

This is the issue:

Car stiffens up: -steering gets too stiff, -car gets sluggish acceleration, -very hard to break, -rough ride.
This caused me to get into an accident few months ago, as the car becomes very tiring to drive when it is like this.
But here's the really weird part, after a week or so, it goes back to normal. How can a problem like this correct itself?
Its like I'm driving two different cars.
I tried to alter tire pressure, no effect.

What could be wrong?