"My seizures decreased with treatment."

It may be okay to say it in speech, but it's to be avoided when writing, because it is ambiguous.

"Tedavi ile nöbetlerim azaldı" can also (and does normally) mean: "My treatments as well as my seizures decreased." It would be understood as the shortened form of: "tedavilerim ve nöbetlerim azaldı".

Furthermore, for me, it just sounds better to put the adverbial part "tedavi ile" next to the verb.

added now

it is a very weird word order. Maybe you can hear it in a poem but not in a normal sentence. Place your verbs at the end