If you are average in your level, and move one level up, you will suck at that level. You will probably be below average and struggle. <- Important keyword
When you move back to your level, you will be above average. Your teammates will feel slow, you can anticipate/read read the game much better... etc.. etc..
It seems that 'struggle' at the higher level, forces players to learn much faster. It can have un-intended consequences in some though (give up playing). You, when going a level up, it has to be a level you can still manage.
eg. a 9yo (second grade), could manage to play with 10yo (third grade), but would never be able to cope with 11-12+ yo (fourth grade)
If you are an adult recreational player, you could move from lower-intermediate, to upper intermediate, but you will flame out at a semi-competitive level.