Dario Argento's Phenomena, edited for the US market under the title of Creepers.

The story revolves around Jennifer Corvino (Connelly), a girl who is a schizophrenic sleepwalker and has the ability to be able to communicate with insects via telepathy. Being the new girl at her school and sleepwalking the first night she's there gives her fellow peers ample ammunition to bully her. Parallel to that the pupils at the school are being terrorized by a psychotic assailant who decapitates their victims. These crimes are being investigated by one Inspector Rudolf Geiger (Patrick Bauchau) and his assistant Kurt, a cameo role by Michele Soavi.
Jennifer unsurprisingly befriends budding entomologist Prof. John McGregor (Pleasance) who has an intriguing little helper monkey. Serving as a possible inspiration for Romero's Monkey Shines (1988). Jennifer then sets out using her psychic ability to pursue the killer.

Phenomena appears to be Argento's attempt to amalgamate elements of De Palma's Carrie (1976) and any number of Gialli - a mix that sounds good in theory but doesn't quite come together so well on-screen, but at least it looks good.

Featuring a chilling performance from Daria Nicolodi, who plays Frau - the mother of a hideously deformed boy. Not to mention an equally good performance from an incredibly young Jennifer Connelly and Donald 'don't call me Dr. Loomis'Pleasance being...well Donald Pleasance. Memorable moments include a swimming pool full of maggots, gratuitous decapitations and of course a razor wielding monkey, standard. I'd also like to compliment the beautiful cinematography.
The soundtrack contains a musical score by Goblin and in contrast to that metal tracks by Iron Maiden and Motorhead, a theme Argento would later (overly) use in Opera (1987).

See this for the lunacy, please.