"Both rushed to mum and were able to help - she was at the hospital within 10 minutes."
Mrs Hyslop, from Wellington, was taken to Taupo Hospital before being airlifted to Waikato Hospital with critical injuries. Mr Hyslop said his mum was on holiday in Taupo with her husband Bill and some family friends.
The group was looking forward to the Huey Lewis concert being held today at the Riverside Park and Union Amphitheatre.
He said the whole incident was "catastrophic".
"It was a hell of a thing to happen. It is easy to start questioning why the trailer came off in the first place and why it had to be her that was hit but that doesn't help so we are just trying to focus on her recovering."
He said the family was trying to stay positive about her recovery.
"Everyone has had their moments. I am in a much better headspace today, I feel like she's going to be fine. She's pretty tough and after everything she still looks amazing.
"Mum has been sedated for the most part but she has been squeezing people's hands which has to be a good sign.
"At this stage we are just waiting to see how she progresses, we'll probably know more by Sunday."
Mr Hyslop described his mum as a "steady person" who was always lovely and loved her chardonnay.
"I have an amazing relationship with mum - we share the same sense of humour and always have good banter. When my humour gets a bit dark she always tries to lighten things up.
"She loves reading - she can finish a book in a couple of days and is always the first person on the dance floor, doing the twist."
Taupo Police Senior Sergeant Fane Troy said an investigation into the incident was ongoing and it was too early to say whether charges would be laid.
