It is the fear every rugby player puts to the back of their mind when they cross the white lines, but it became very real for Keith Earls last month.
The Munster star collided with Ireland colleague Eoin Reddan's shin in an innocuous incident during the closing stages of the inter-provincial derby at Thomond Park on December 27 and lay prone as play went on.
The medics spotted something serious right away and raced to his aid. When the game came to a long standstill, an eerie silence descended on the Limerick venue as the local hero remained prone for a number of minutes.
Eventually, he was placed in a neck brace and on to a mobile stretcher and the entire stadium breathed a sigh of relief when he raised his hand and gave a thumbs-up to the reception he was receiving from both sets of fans.
That put the minds of those watching at ease, but while it indicated he was OK leaving the pitch, Earls has revealed the very real fear that flashed through his mind when he went down initially.
"Whatever way I landed, I think I hit Redser's shin and I heard a crack in my neck," he recalled.
"I thought about my kids straight away. I said I better lay still here. The lads got out to me then and went through a few bits and I could move my hands. I didn't have any weird feelings just a small bit of tightness in my chest but I think that was more like a panic attack after hearing the crack in my neck.
"It was scary hearing the crack. My father, if he had hair he would have lost it. I could see when he came down to see me he was devastated. I gave them all a bit of a fright but thankfully it was all good."
In the end, the panic was short-lived and he was able to communicate the message that he was OK through his hand movements.
"I stayed still but I moved my hands," he said. "It was just like getting a nip off a physio or a chiropractor on a joint in the neck.
"Thankfully, everything was fine. I told them I was fine and could I get up but they said 'no once you've heard a crack we're not going to let you'."