Some anesthetics impair memory even while still conscious

When a high enough dose of an anesthetic agent is administered, information from the outside world is not processed by the patient and, thus, no conscious memories are formed. In this sense, all anesthetic agents are amnesic at a certain dose. Subsequently it became known that benzodiazepines at lighter levels of sedation also produced a lack of later recall. This was the first group of drugs to exemplify the difference of amnesia from sedation. The term ‘conscious amnesia’ is thus a more appropriate description of this drug effect. Our work has demonstrated that propofol produced virtually identical conscious amnesia as the benzodiazepine midazolam. Characteristics of conscious amnesia included relatively minor sedation, apparently normal cognition, and most notably, a lack of memory for events occurring when effective concentrations of propofol or midazolam were present. Conscious memory is also referred to as explicit or episodic memory, and is characterized by recollection of events or items within a context of time and place.-link

The drug versed(midazolam) and propofol, can cause conscious amnesia.   Some people would rather have bad memories than no memory at all, and if these are given for surgical procedures the gap in time created in memory can be distressing and even traumatic.