Stiff brake pedal after jump-start.

Hello, i forgot the light inside the car on, and the 12V battery died.
After jump-starting, the brake pedal is stiff. I can still hear the brake motor when I open the door.

Any ideas what I can do before going to the service?

I think, the problem is in jump-start procedure: i connected it to another car for just 5 minutes, then disconnected it, and when I started the car. The headlights automatically turned on, and the battery died very quickly. During this 5 seconds, i saw lots of errors on the panel, but I guess is expected, since car didn't have enough power to turn on.
Then I reconected the jump-start cables , and just started the car with them attached. Without any problem or error light, except this stiff pedal.

Thanks.

 

Thanks, i started the next day the car, and it just works.
I guess, the problem was that the 12V battery was flat.

Thanks!