How safe is conscious sedation ?

Very: when provided by a competent anesthesia provider. Conscious sedation is performed thousands of times every day in the US.

It is highly safe: Oral conscious sedation is safe. On healthy patients IV conscious sedation is often one of the safer and most effective forms of administering dental sedation since the medication is injected directly into the bloodstream. At any time an antidote can be administered to reverse the effects of the medications if necessary.

Safe and effective: Conscious sedation is safe and effective for patients who need minor surgery or a diagnostic procedure.