The Ryder Cup teammates are both on eight under par and joint third, just two behind American David Toms at the halfway point in The Players Championship at Sawgrass.
Northern Irishman McDowell spoke after his 69 about what went through his mind during his recent run of three missed cuts in four starts that began with a round of 80 at Bay Hill.
"I just couldn't piece anything together and you have crazy thoughts," the US Open Champion said.
"Will I ever win again? Will I ever be in contention again? Am I done? Am I finished?
"I don't think I gave that thought any seriousness, but it flashes through your mind.
"I think everything flashes through. I sacked everyone, re-hired them, probably sacked them again.
"It's just the craziness of this sport, you never really know what's around the corner.
"That's why we love this game, it's why we hate it and it's why it keeps us coming back for more."
A weekend with coach Pete Cowen has put him back on track and after closing with a superb birdie at the 18th, he added: "I've worked hard on this slightly new version of my swing and it feels good to be going out there and executing shots under pressure and looking forward to being in the mix."
The World Number One spot is out of reach for McDowell over the closing 36 holes, but not for Donald.
He needs to win to overtake both Lee Westwood and Martin Kaymer, but the WGC-Accenture Match Play champion has yet to drop a stroke and, after birdies at the 16th and 17th, parred the last for a superb 67.
Donald said: "It's very satisfying not have any bogeys so far. I played better today, the 14th was the only hole I struggled on.
"There was a lot of grind yesterday and today was more a cruise-control day.
"Hopefully I'm stepping up and getting better. I obviously gained a lot of confidence from my win and I feel good about my game.
"My short game's been good for a couple of years, but now I'm starting to hit more fairways, more greens and give myself more opportunities."
Former US PGA Champion Toms became the man to catch when he followed up his first day 66 with a 68 to stand ten under.
He was one in front of first day pacesetter Nick Watney, who added a 71, and two ahead of not only McDowell and Donald, but also Steve Stricker and last week's winner Lucas Glover.
Londoner Brian Davis would have been on the same mark had he not double-bogeyed the fourth - he hit his approach into the water on what was his 13th hole - but he came back with two birdies for another 69.
"The wind was swirling a bit and I'm happy with where I am," he said. "I was a little bit down and my caddie was whacking me on the backside."
Phil Mickelson, who would also go to number one by claiming the title, climbed to six under with a sparkling back nine of 31 featuring an eagle putt of almost 40 feet at the 16th, but then came home in 40 - only two better than Tiger Woods managed before quitting on the opening day.
That meant a second successive 71 for Mickelson to leave him two under and deep in the pack.
Ian Poulter lost ground when a 72 kept him at two under, the same as Scot Martin Laird and 18 year old Matteo Manassero.