I lost against Brok, i did beat him luckily after that but it's bothering me. I hope there isn't any stats that shows that i have lost against him. So do i lose anything or does it affect my game somehow? Thank you already for answering!

when all of your pokemons fainted, you lose 5% of pokedollar (in-game money shown on bottom left), that's all

Nahh u don't lose anything in npc battle until u black out against npc u only loses some of ur poke$ only so there is no problem if u lose some of npc

Well, you do in a way, when you face your opponent again, you wont receive any exp from the battle, so you may end up loosing out on extra Exp you could have earned.

You lose a ton of money if you lose against the jesse and james boss :/