The latest Home and Away episode to air on Network Seven in Australia saw Dex at the centre of a horrifying road accident after borrowing his sister Indi's car.
As Indi's brakes had been tampered with by her vengeful love rival Ruby Buckton, Dex lost control of the vehicle in explosive stunt scenes.
Upcoming episodes will see Dex's life hang in the balance as he receives emergency treatment in hospital.
Cottier told Home and Away's official website: "Get ready for the biggest thing ever to happen to my character and one of the biggest things to happen on the show for a long time. It's massive - you're going to be weeping like I was!"
The actor also praised Home and Away's team for the "fantastic" crash sequence, which was filmed with a stunt double before Cottier was brought in for the aftermath scenes.
He said: "The car landed upside down, which is perfect because Dex is trapped in the car. I was in this upside-down car, so it was really hot. It was kind of a good experience at the same time!"
Meanwhile, writing on his Twitter page after the broadcast, Cottier said: "I'm ok people. Big few weeks coming up for Dex though....gotta pull through this $h!t man! Nice to know you all care though. Make sure you all keep watching to see if dex will make it through the next couple of weeks! (sic)"
Home and Away fans in the UK will see the crash scenes on Channel 5 in October.