Yes, can poison you. Yes, Fluoride in any form, if ingested, can be overdosed on. If too much Fluoride is swallowed it can even cause death. It is best to always follow the written directions on the bottle or the instructions you are given by your dental care provider.
Patient support. Usually the affects of Fluoride overdose is being sick to your stomach. Vomiting and or diarrhea. Supporting the patient with fluids and meds for nausea.