When you eat too much celery it can lead to malnutrition due to it's low calories but you'd have to eat nothing but celery and eat way too much of the celery for it to be a problem.
The average person would not even want to consume enough celery that could become toxic to them so you're safe snacking on celery daily.
Celery is high in fiber too though so when eaten too much the fiber in the celery could lead to diarrhea, gas and bloating.
You're unlikely to ever eat enough celery for it to kill you though.