That would make him mentally unstable at best, and among other things "Borderline Personality Disorder; with a dash of Schizophrenia".
Hearing voices, and having the desire to act on them is exactly what I stated above. I know this how? My sister suffers from both of those at least, and trust me, she's like a light switch. One moment normal, then ranting and violent the next. They can actually act normal as they fight the voilent urges and voices in their heads. Just not all the time obviously. Toss in another ingredient which could potentially glaze that stick of dynamite, Manic Depression with Bi-Polar, and it's locked in. You cannot mess with that unmedicated personality for long.