Kvitova had won Wimbledon twice in the last four years and had never failed to make at least the quarter-finals in her last five visits to south-west London.
But she has endured an erratic spell since thrashing Eugenie Bouchard to regain the All England Club crown 12 months ago.
The 25-year-old Czech’s spluttering form took a turn for the worse on Saturday when, leading by a set and 4-2, she suddenly went into a total meltdown, allowing Serbian 28th seed Jankovic to claim a surprise 3-6, 7-5, 6-4 victory on Centre Court.
Kvitova, who has now bowed out of the last four Grand Slams before the quarter-finals, had fallen in love with Wimbledon since first winning the grass-court Grand Slam in 2011.
“I said many times that it’s something really special to be Wimbledon champion. That’s why I’m playing tennis. I was the lucky to win it here,” Kvitova said.
“So it’s not great to lose in the third round. Not to be in the second week of the favourite tournament for me is really sad.
“It’s not easy to go away. I think it’s going to take me few days, few weeks maybe (to recover).
“But that’s how it is. It’s tennis. I’m still human. I’m not a robot.”
Kvitova plans to get away from tennis for a while as she comes to terms with the end of her Wimbledon reign.
But the downhearted Kvitova conceded that even time with her nearest and dearest wouldn’t be an immediate salve for her wounded pride.
“First of all, I’m coming home to see my family and friends,” she said. “But I’m just probably going to need some time.”
Kvitova had already taken two months off earlier this year after losing her passion for sport and arrived at Wimbledon still recovering from a virus that forced her to pull out of the warm-up event at Eastbourne.
She said she was still feeling the after-effects of that illness against Jankovic.
“I didn’t feel 100 percent, for sure. I was still kind of struggling a little bit with the movement,” she said.
“I was still missing a few shots. The timing really wasn’t the best.
“For sure I wish to feel better. But this is how it is.”
Kvitova will have a chance to rescue a frustrating year at the US Open in August.
But she has never been past the last 16 in eight visits to New York, prompting her to give a cautious assessment of her chances in the year’s final major.
“I need to be positive and think a little bit better about the U.S. I can play on the hard courts, for sure,” she said.
“I just need some practice to feel well in the US Open, which I really didn’t before.” – Agence France-Presse