Don't be sad, this happens to me almost every season in almost every game.. tactics (I tried many of them) are working fine, you are quite high in the table, but then suddenly, one day with no reason (morale, form, players, motivation - everything is high) you began to lose in every single game, just constantly. I got used to it, because I am not sure, I can change it whatever I do. Quite satisfying is that other teams usually don't win everything too, so the final results aren't that bad. But you can definetly drop a few places and that's really bad if you are playing for play-off or something like that.
Of course, every team can lose, but this is weird. With no reason you can't win for example in 10 matches, although everything is working. I think that it is a specific mechanism in the game, that makes it harder for you and test you as a user (as Mightytigers said). But if it is so, it is really stupid - it shouldn't be mechanism. In reality you usually lose 10 matches for some reason. So I agree with you. This happens very often and it sucks. Especially when you are favourite of the competition, you are first and suddenly lose 5 home matches in row with teams that are already relegated or placed 15th to 20th...oO)