355 Brake pedal acting strangely...

Hi,
it's been a month since my last drive with my 355.
Tonight, after leaving my parking and driving few minutes (where everything was normal) after a stop, suddenly the brake pedal acted strangely.

I don't know how to properly describe it, it was like there was a notch and the pedal rebounds on it when lifting the foot from it.
Very strange, never had this in any of my cars.
So I touched it few time and it did the same and then the brake light turned on.
I decided to come back home, but just before I pushed very hard on the pedal a couple of times: the light when off and the pedal acted normaly again.
So I went for my drive on the highway: brakes were absolutely perfect.

Does anyone have any idea of what happened to me tonight?
Something stucked (ABS related maybe?).

Thank you.

 

No I didn't, but I will.

 

Brake fluid level is perfect.

Any other idea?