Barnaby Joyce has arrived back in Canberra, after video emerged of the Nationals MP lying on a Canberra pavement talking loudly into his mobile phone.
Video published by the Daily Mail showed the shadow cabinet member on the ground in the inner suburb of Braddon after sitting on a planter box and falling off.
The video, which has since gone viral, has led to questions about the former deputy prime minister's fitness to sit on the opposition front bench.
Mr Joyce, arrived into parliament almost an hour after question time began on Monday, ahead of a Nationals party room meeting.
The Nationals MP said he admitted he had made a mistake.
"Look, obviously I made a big mistake," Mr Joyce told Seven's Sunrise program on Monday.
"There's no excuse for it.
"There's a reason ... they say certain things happen to you if you drink (while on medication) and they were absolutely, 100 per cent, right."
Nationals leader David Littleproud said Mr Joyce had matters he needed to work through but hoped he would return to work in the afternoon or later in the week - though the party's meeting is planned for Monday.
"This is something that he's deeply embarrassed about," Mr Littleproud told Sky News.
"He's made that very clear that this isn't normal behaviour that he undertakes and there are extenuating circumstances surrounding that and obviously, we will support him in making sure that, anything that he does need, he gets."
Mr Littleproud had previously said he would talk to Mr Joyce about the conduct seen in the video, as well as his position on the opposition frontbench.
The government has called on the coalition to answer for Mr Joyce's actions, with Finance Minister Katy Gallagher saying the situation was "incredibly sad".
"These things do nothing for the profession of politicians ... it confirms, in people's minds, the public's minds, negative association with politics, and I think that's a real shame," she told ABC radio.
"But personally, I hope he gets the help he needs because it's a very unusual position for someone of that age to be in."
Labor MP Tania Lawrence said the behaviour of the Nationals MP was embarrassing.
"We are examples to our community young and old, we represent Australia to the international dignitaries and visitors we meet each week," she told parliament.
"We are under the spotlight, and we should act accordingly, and if we can't, then we must also be able to understand that there isn't a single member here who is irreplaceable."
