primedice if fair but sometimes i lose 50% chance bets 10 times in a row
This is very usual after a certain amount of bets.
I have already seen several losing streaks which were much longer than 20 in a row.
That is like flipping a coin. If you flipped it thousands of times, there is a good chance that you will see heads or tails come up 10 times in a row.
The exact probability of that happening can be found on google. I don't know the exact equation...