As a result, Lehan says sleep studies show Kiwis are "really shortchanging ourselves" and getting six hours or less.
The consequences, says Lehan, include excessive sleepiness and succumbing to high caffeine intakes.
While we're under the impression we should be aiming for eight solid hours a night, the real key is getting yourself into 90-minute sleep cycles, five times a night.
That's "from our light sleep through to a deep sleep in our REM sleep or a rapid eye movement dream state," explains Lehan.
"That's where we get this sort of magic number (of) seven to nine hours."
You may be reading this and thinking you've been getting along just fine on five-and-a-half hours a night but, while everyone is different, there are some important things to know about what happens when you don't get enough sleep.
You need sleep to heal, repair and grow
"If you're not getting enough of those complete sleep cycles you don't have enough time for your body to heal and repair and grow and do all those good things."
Lehan tells Morrison there are parts of the brain that are working as we sleep. We "consolidate memories and our brain decides what are we going to keep; what's useful information."
And this is when our immune system works to fight diseases, too.
So, this is where the requirement of five rounds of 90 minute sleep cycles kicks in: "We have to have enough complete sleep cycles in order for our body to do all those good things ... the brain detoxification, the memory consolidation, the healing, the growing and all of that sort of thing."
What a lack of sleep is doing to your waist line
For those of us who don't get enough sleep, as well as making our way through the world bleary-eyed, we're also at more risk of obesity, diabeties and mental health conditions.
"Cardiovascular disease is very, very strongly linked to poor sleep," adds Lehan. So it really is something we need to take very very seriously. If we're not getting a good night's sleep it has much greater consequences than just feeling tired the next day."
What can you actually do if you're a troubled sleeper?
For the ordinary person, Morrison asks how one can "take life back" to get more sleep than what they're probably getting right now.
Lehan's tip is to, firstly, "think about the last time you were on holiday" and weren't beholden to waking up by an alarm.
Work out how many hours you slept for in order to wake up feeling fantastic. And that's your benchmark.
To bring this number into your everyday working life, Lehan explains you need to work out what time you need to be up and out the door and count yourself back from there.
"So once you know that then you start saying, okay, well if I've got a non-negotiable when I'm at work. I have to get up at six. Then let's start working backwards and say well does it mean I need to be in bed asleep by 10pm? Does it take me about 20 minutes to fall asleep? So, therefore I need to think about that. I need to go to bed half an hour earlier so I can drift off to sleep. If I wake up multiple times during the night, then all those awakenings add up to sleep loss as well."
But how do you achieve this when you've got kids and commitments and a haywire schedule?
It's not easy, admits Lehan. She says many of us are guilty of opting for one more episode of a Netflix show rather than turning off everything in order to get your hours of sleep in.
"You have to make a conscious decision to do something and then stick to it. So you'll feel so much better for it. And that's the great thing. The more sleep you get, the better you feel."
Take Life Back: Listen to Stacy Morrison's full interview with Rachel Lehan here:
