"He was extremely intoxicated with liquor and tablets when we took him in," police duty officer Hans Nilsson told the Expressen newspaper.
The 22-year-old Sweden Democrat entered the Riksdag in September as representative for Dalarna County in central Sweden.
He had previously been active in the far-right party's youth organisation and served in the local council in Borås in western Sweden.
On Saturday night, Petzäll showed up at a party in a flat in Trelleborg in southern Sweden that he shared with his ex-girlfriend. According to Expressen, the relationship ended several months ago.
The second time police showed up at the party after receiving calls about a disturbance, they found Petzäll drunk in the stairwell outside the flat.
According to police, he had damaged various objects and the interior of the apartment, the Aftonbladet newspaper reports.
Petzäll was also so intoxicated he was first taken to the emergency room before spending the night in a police station jail cell to sober up.
He later claimed the damage to the apartment occurred when he accidentally knocked over a television, but his actions have met with disapproval from his fellow Sweden Democrats.
"What happened is obviously unacceptable. As one of the party's Riksdag representatives, one must always exercise good judgement," the Sweden Democrats' deputy Riksdag group leader Sven-Olof Sällström said in a statement.
"We've come to an agreement with William Petzäll that he immediately take a timeout from his political duties and that he seek help in order to deal seriously with the factors which lay behind the incident."
According to Sällsröm, Petzäll is now on sick leave from his role as a member of the Riksdag. He added that Petzäll isn't suspected of having committed any crime.