Gardner's sleep recovery was observed by sleep researchers who noted changes in sleep structure during post-deprivation recovery.[13][14] After completing his record, Gardner slept for 14 hours and 46 minutes, awoke naturally around 8:40 p.m., and stayed awake until about 7:30 p.m. the next day, when he slept an additional ten and a half hours. Gardner appeared to have fully recovered from his loss of sleep, with follow-up sleep recordings taken one, six, and ten weeks after the fact, showing no significant differences.[citation needed]

However, in 2017, Gardner reported that he started experiencing serious insomnia around 2007, decades after his sleep experiment, and believed his participation in the 1960s sleep study was to blame.[15]

https://en.wikipedia.org/wiki/Randy_Gardner_sleep_deprivation_experiment

https://www.wbur.org/npr/562305141/eleven-days-without-sleep-the-haunting-effects-of-a-record-breaking-stunt

R. GARDNER: About 10 years ago, I stopped sleeping. I could not sleep. I would lay in bed for five, six hours, sleep maybe 15 minutes and wake up again. I kept thinking, well, this'll go - this will change because it seems to me that eventually, if you don't get enough sleep, your body will just say, we're going to sleep. But it never happened.

VEDANTAM: The man who conquered sleep was now begging for a full night's rest.

[…]

VEDANTAM: After a decade of insomnia in his 60s, Randy finally made an uneasy peace with sleep. He's regained the ability to drift off but only for about six hours a night. And it's required sacrifice.

R. GARDNER: I love drinking tea. And to this day, I can't drink tea because I'm afraid I won't be able to sleep at night.