The nights that don't cool off
If you've woken up at 3 a.m. this week with a headache and a dry mouth, you're not imagining it. El Segundo usually gets a break from real heat because of the marine layer rolling in off the water, but during a heat wave that layer thins out or disappears for a few days, and the ocean stops doing its job. Nights that are normally in the low 60s sit in the low 70s instead, and a lot of houses in this town were built assuming that cool night air would do the work of resetting the place. When it doesn't, the house never really recovers before the next hot day starts.
Why older El Segundo homes hold heat
A big share of the housing stock here dates from the 1940s through the 1960s, small bungalows and post-war tract homes with little or no attic insulation and single-pane windows. These houses were built for a climate that rarely asked much of them. They don't have the thermal mass or the sealed envelope that newer construction further inland uses to fight heat. Once the walls and the slab soak up a few days of 85-plus afternoons, they radiate that heat back into the bedrooms all night. Add a west-facing bedroom window catching the late sun, and you've got a room that stays warm long after sunset, whether or not you have air conditioning.
More on this from Lively Drops in El Segundo.
What heat actually does to sleep and energy
Your body needs to drop its core temperature by a degree or two to fall into deep sleep. A warm bedroom fights that directly, so people get lighter, shorter sleep during heat waves even if they don't wake up formally. On top of that, most people sweat more than they realize during hot weather, including overnight, and they don't drink enough to replace it because they're asleep or not thirsty yet. That combination, poor sleep plus mild dehydration, is what produces the flat, foggy, low-energy feeling that shows up two or three days into a heat wave. It's not just tiredness. Dehydration thickens the blood slightly and makes the heart work harder to move it, which is part of why people feel sluggish and get headaches that a nap doesn't fix.
What you can check yourself
Start with the house before you start with your body. Close blinds and curtains on west and south-facing windows by early afternoon, before the sun hits them directly. A box fan in the window in the late evening, pulling cooler outside air in once the temperature drops, can do more than people expect in a house this size. Check your bedroom is actually below the level in the rest of the house. Ceiling fans should run counterclockwise in summer to push air down. On the body side, a plain habit that works is a glass of water at the same times each day rather than waiting for thirst, and paying attention to urine color as a rough gauge. Dark yellow in the middle of a heat wave is a signal to drink more, not a coincidence.
When it's more than a bad night's sleep
Mild dehydration is a homeowner problem, solved with water, shade, and airflow. It stops being that when the symptoms don't track with a normal bad night: confusion, a racing heart at rest, dizziness on standing that doesn't clear in a few seconds, or someone who has stopped sweating and feels hot and dry. Those are signs the body's cooling system is failing, not just running behind, and they call for medical attention, not another glass of water. For people who are otherwise healthy but badly depleted after several rough nights in a row, and who aren't recovering with normal fluids and rest, a medically supervised IV hydration can correct the deficit faster than drinking alone, because it bypasses a gut that may be sluggish from heat in the first place. That's a decision for a clinician, not something to arrange on your own, but it's worth knowing the option exists between
drink more water
and
go to the emergency room.