could be wrong here, but it looks like you stop the sound on a key down and start it on a key up...
I expect when you press the key for the first time, it tries to stop nothing, the id is null as it hasnt been initilised???
Read it a bit more, above is wrong, but you are in a loop, how many times does the event keydown pass, stopping a stopped sound is probably not good, also, you may be staring dozens of new sounds???
al_play_sample(overworld, 1.0, 0, 1, ALLEGRO_PLAYMODE_LOOP, &id);
wait for 10 secs (using the allegro timer),then stop it.