Bernard Foley has revealed the depth of his torment after finally being cleared for a Super Rugby comeback after five weeks battling post-concussion symptoms.
Foley returns for the desperate Waratahs' derby with the Rebels in Melbourne on Friday night in a new-look backline - featuring Israel Folau at fullback and Jake Gordon making his starting debut at the expense of relegated Wallabies No.9 Nick Phipps.
In the biggest shake-up of his two-season tenure as head coach, Daryl Gibson has made six positional changes to the backline after the Waratahs' worst-ever start to a campaign.
Winger Reece Robinson is the only player to remain in the same position as he was in last Saturday night's 28-12 home loss to the Brumbies, with Rob Horne moving to outside centre to accommodate Folau at fullback.
Andrew Kellaway shifts from fullback to Horne's old wing spot.
"At the moment, that backline's not clicking so we decided we had to make those changes in search of a better outcome," Gibson said on Wednesday.
But having his Wallabies playmaker back - a selection no-brainer - is Gibson's biggest inclusion.
"I'd hate to see our win percentage when Foley's not playing. Certainly he's a big bonus to the team," Gibson said.
"He's onto the ball well and gets the attack flowing, so it's good to have him back."
Mindful that former All Blacks Charlie Ngatai and James Broadhurst had been forced to retire after suffering similar post-concussion symptoms, Foley admitted at times the uncertainty around any possible return was a killer.
'It's quite a scary injury in that blokes can get knocked and not come back from it," the 27-year-old said.
"They can be innocuous or they can be the prone knockout. No-one really knows about this issue.
"There's no deadline or guideline as to how long before you're going to be back."
Initially, the 41-Test star was light sensitive and left irritated by watching TV, computer screens or even checking his phone for any length of time.
Some days Foley would wake up feeling fine, other days lousy. The same after training sessions; he'd pull up well one sometimes, and endure headaches on other occasions.
"That was probably the frustrating thing. The things that were lingering," Foley said.
"Head injuries are something very serious and something very relevant at the moment, I suppose, with the way it's been handled in rugby league and rugby union.
"The player's welfare is paramount in terms of making sure people are safe and right in going back on (the field).
"It was disappointing this number of weeks and not being out there but I'm eagerly looking forward to Friday night.
"I've been put through two weeks now of full contact and everything so I'm fully confident."