Apart from the previous season when Bayern Munich failed too much, in the other seasons they tend to win most of the time and lose few games and the teams that defeat them used to be those in the middle of the table like Hoffenheim and the others. I wouldn't be surprised to see them losing against Mainz this time and they still have some security gap.
Dortmund is the one that is suffering a lot in Bundesliga this season and should try to fix things otherwise they will be out of all European competitions..