“I Slept the Fast Away!” Why Fast Days Mess With Our Sleep (and What to Know About It)

Fast days are strange — we do almost nothing, and yet somehow we can’t fall asleep when they’re over.

Right after the fast ended, I got a call from my teenage son, Dovid. He’s in camp in the Catskills, and I could hear him sipping (loudly) on his favorite post-fast treat — a freezing cold Ice Cap. It had been a sweltering, sticky day upstate, and I asked him how the fast went.

“Great!” he said, full of pride. “I woke up to daven Shacharis, went right back to bed, and my friends woke me up for Mincha. I basically slept the fast away!”

Only a teenager could pull that off.

Meanwhile, the rest of us spent the day doing very little — from couch to bed, maybe checking the clock a hundred times — waiting for the fast to end. Then the moment we finally eat, instead of feeling ready to sleep… we’re completely wired.

Why Can’t We Sleep After a Fast?

Let’s be honest for a second. We all know what we should break our fasts with — something gentle and balanced, a warm drink, maybe soup, maybe a banana.

But let’s be really honest:

I want my coffee — or coffeessss — and a large piece of kokosh cake… followed by another one.

And I’m not the only one.

Between the sugar, the caffeine, and the carbs, we go from empty to overloaded in about 10 minutes. Add in the fact that we barely moved all day and suddenly we’ve got energy, stimulation, and a digestive system working double shifts — all after 9:00 PM.

Here’s the science behind it:

1. Blood sugar spikes: When you eat a big sugary or carb-heavy meal after fasting, your blood sugar shoots up quickly, then crashes later. This rollercoaster can make your brain feel alert just when it should be winding down.

2. Circadian rhythm disruption: Our body clock, or circadian rhythm, relies on regular eating and sleeping patterns. When we fast and then binge eat late at night, it sends mixed signals to our brain’s sleep center, confusing it and making it harder to fall asleep.

We’re not tired — not because we’re so rested, but because our bodies are confused. Between the cake, the coffee, and the lack of activity, our systems don’t know what hit them.

Before a 25-Hour Fast? Same Story, Other Side

Next up is a 25-hour fast — and this time, the struggle can start before the fast even begins.

We overeat and overdrink at the pre-fast meal thinking we’re stocking up. But instead of “preparing,” we just end up bloated, uncomfortable, and up all night running to the bathroom.

Here’s the secret: less is more. Hydrate through the day, not all at once. Eat regular meals, not super-sized ones. Your body isn’t asking you to prepare for battle — just to stay balanced.

So What Can We Actually Do?

Honestly? Just know what to expect.

You might not sleep great after a fast. You might be tossing and turning at 1:00 AM wondering how a slice of cake turned into three. But that’s okay.

This morning, Dovid called me again. He told me he finally fell asleep at 3:00 AM — that Ice Cap hit hard — but he still got up, davened, and was determined to get the day (and his circadian rhythm) back on track.

Here’s a confession: even as a sleep coach, I’m human. Even though I know that cake and coffee aren’t great for sleep, sometimes I choose them anyway — because life is about choices, and that’s empowering.

That’s exactly why I was so proud of Dovid. He made the choice to indulge — loudly and unapologetically — and then he got it together. He still managed to get up the next morning, daven, and get on with his life.

The real power is in what you do next: get back on schedule.

Even if you fell asleep late, don’t sleep the whole morning away. Don’t drag it into the next day (and the next…). Get up, get dressed, daven, eat breakfast — get the rhythm going again. That’s how you reset.

Resetting your sleep rhythm after a fast isn’t all that different from recovering from other disruptions. Just last week, I wrote about why jet lag hits hardest when you get home — like after a trip to LA — and how important it is to get back on schedule. Whether it’s fasting or traveling, our bodies thrive when we honor consistent routines. Read more here →

The Morning After (and Why It Matters)

I laughed and told him he’s officially a sleep coach-in-training.

Honestly, that call made my day — not just because I was proud, but because it reminded me that we’re all figuring this out together. Fasts are weird, bodies are weirder, and sometimes your best post-fast strategy is to eat the cake, stay up too late, and try again tomorrow.

It’s not about perfect sleep. It’s about getting up the next morning and choosing to reset — one groggy, caffeine-fueled step at a time.

Want to Sleep Better and Feel More Energized?

Whether you’re dealing with disrupted sleep, racing thoughts, busy schedules, or just want to improve your rest, I’m here to help. Let’s work together to create a plan that fits your life and helps you feel your best every day.

Book a free 30-minute sleep coaching consultation with me here: https://calendly.com/chevymermelstein/30min