How is deep sleep and REM affected by hormonal fluctuations?

Ever notice how some nights you sleep deeply, and others you’re restless, dreaming wildly, or wide awake at 3 a.m.?

That’s not random, it’s likely to have something to do with hormones.

PSA: If you track your cycles - which I highly recommend you do, log these nights and track their cyclical correlation!

The fluctuations in oestrogen and progesterone throughout your menstrual cycle affect your sleep architecture: how much deep sleep and REM you get, how easily you fall asleep, and how rested you feel the next day.

So we're going to break down the science, phase by phase.

Menstrual phase (days 1–5):

Deeper sleep, increased need for rest

At the start of your cycle (when your period begins), both oestrogen and progesterone are at their lowest. This drop can actually allow for more deep sleep, particularly in the first couple of nights. However, because your body is using energy to shed the uterine lining and manage inflammation, you may still feel physically drained.

What’s happening:

• Body temperature drops - lower core body temperature → supports deeper sleep

• But, increased prostaglandins → can cause cramps or discomfort, which may interrupt sleep for some

Support it: Prioritise rest, magnesium-rich foods, and gentle movement. If you're especially fatigued, it's not laziness—it's biology.

Follicular phase (days 6–13):

Lighter sleep, more mental energy

Oestrogen begins to rise steadily in this phase, promoting alertness, motivation, and cognitive sharpness. It also tends to lighten sleep, reducing the amount of slow-wave (deep) sleep.

What’s happening:

• Higher dopamine and serotonin → better mood, easier wake-ups

• Shorter deep sleep stages → you may feel fine, but sleep is less restorative

Support it: Maintain consistent bed and wake times. Get morning sunlight and avoid overstimulation late at night (yes, including scrolling).

Ovulatory phase (Days 14–16):

More REM sleep, vivid dreams

Around ovulation, oestrogen peaks leading to increased REM sleep, the dream stage associated with memory processing and emotional regulation. (Your time to journal your dreams and things that come up!)

Though this can mean more dreams (with REM), sleep may also be lighter, with more night-time wake-ups (temperature increase).

What’s happening:

• Peak oestrogen → increased REM density

• Slight body temperature rise post-ovulation → may disrupt sleep for some

Support it: Stick to cooling night routines (room temp, breathable fabrics). If you’re waking feeling mentally tired, consider this your cue to support your nervous system with deeper wind-downs.

Luteal phase (Days 17–28):

Less REM, more disrupted sleep

After ovulation, progesterone rises. In early luteal days, this hormone can have a mildly sedating effect, helping you fall asleep faster.

However, as both oestrogen and progesterone decline in the late-luteal phase (after ~Day 21) (the PMS window), sleep often becomes more fragmented.

What’s happening:

• Dropping progesterone → more night wakings

• Less REM sleep → can affect mood, focus, and emotional resilience

• Body temperature remains elevated → may affect how deeply you sleep

• Muscle cramps, bloating, water retention, uncomfortable body feeling → can make it more difficult to get comfy & fall asleep

Support it: Prioritise blood sugar balance (especially in the evening), consider magnesium glycinate or B6, and scale back evening intensity - both physically and mentally.

Sleep isn’t static. Your hormones are constantly reshaping the quality and depth of your rest, especially across a 28-day cycle. You may need more recovery during your period, feel sharper but sleep lighter around ovulation, and experience disrupted or fragmented sleep right before your bleed.

Understanding these patterns makes a difference. You don’t need to force the same bedtime habits every week as your body benefits most when you respond to what it’s asking for.

If you’re tracking your cycle, consider also tracking sleep quality, vivid dreams, or night-time wakings.