Kelli Bannister, 30, from Perth, uploaded the photo to her Facebook account on Tuesday 19 April calling the moment one of the "worst parts of motherhood".
She said she was physically and mentally exhausted as her daughter, Summer, had been poorly for days.
"This moment is real, raw and one of the absolute worst parts of motherhood that at some stage, we will all go through," Bannister wrote on the post.
"The part nothing or no-one can prepare you for, the part where you would give every ounce of your entire being to make your poor baby feel ok again," the mum continued.
"Every cry and every tear makes your heart break just that little bit more and your only wish is that it was you instead.
"I haven't slept in days and am physically and mentally exhausted myself, but as all mums do, we keep going."
Bannister said Summer had been coughing, being sick and "working herself up into a frenzy" all morning.
"My mumma instincts kicked in and I put us both in the shower, with the soothing sound of running water and the warmth touching our skin, she was calm within minutes," Bannister continued.
"Then, my five-year-old came in and snapped this.
"Such a raw emotive moment of motherhood in all her glory... messy bun and all."
The Facebook post struck a chord from mothers all over the world.
"I needed to read this today," one mother wrote. "My almost three-year-old had an MRI under general anaesthetic today.
"Tough moment restraining him while the anaesthetist holds a mask over his face and he's looking and with huge upset eyes."
Another wrote: "I feel your pain. It's horrible when your child is sick and all you want to do is take the pain away.
"Gorgeous photo, motherly love right there."
A dad also commented on the post, praising mums for everything they do.
"It's amazing how as mums you seem to keep going," he wrote.
"Even when you're so burnt out. It's hard for us as dads to watch on and not be able to help with them because all they want is you.
"We worry and we try not to show it. But when it's too much or you just need to sleep - we are here for you."
Bannister's post was shared nearly 2,000 times in two days. After seeing how popular her post was, Bannister wrote an update.
"I just wanted to say a massive massive thank you to each and every one of you for your beautiful comments," she wrote.
"I had absolutely no idea that this image and the story behind it would touch so many people in such a special way.
"Summer is doing much better today and looks to be over the worst."