According to the description here and elsewhere, the maximum difficulty level is 10. Which already means "Impossible - a task that normal humans couldn’t consider" so that's a clue. I have never seen a Numenera roll adjudicated at a higher difficulty level than 10. Even a 7 is getting toward the impossible.
"The upper levels of difficulty, 7, 8, 9, or 10, are all but impossible, since the target numbers would be 21 or higher."
Another clue is provided in the following paragraph (notice that upward mods are not described, only downward mods):
"It’s quite common for players to modify the difficulty of a task. Using training, assets, working together, or–perhaps most importantly–effort, difficulty levels can be moved down multiple steps to make them easier. In other words, rather than adding to the die roll, the number you need is reduced."
By this reading, your dazed character would be rolling against a difficulty level of 5.