The headache that turns out to be dehydration — the long version

On the subject in the title: The headache that turns out to be dehydration — the long version Working notes rather than a conclusion.

Longitudinal report with the method stated, because a number without a method is not a measurement.

Same scale, same time of day, same conditions, 47 weeks. I have also recorded protein intake and resistance-training sessions, both self-reported and both therefore optimistic.

The reason I am posting is a pattern in the middle of the series that I cannot explain and that I suspect is measurement rather than signal.

Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.

The correction was fair and I had been repeating something I had not checked carefully enough.

Lab testing: if symptoms are severe or persistent, checking electrolytes and minerals (sodium, potassium, magnesium, calcium) and interpreting them in context of losses during weight loss is reasonable.

Worth separating two things that the opening post runs together.

Water intoxication: drinking excessive water (more than a few liters per day for extended time) without electrolyte replacement can cause hyponatremia. This is rare but serious. Balance fluid with electrolytes.

Picking up post #2: that is the part I would want checked first.

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

Coming back to post #4, because the follow-up matters more than the original answer.

Orthostatic symptoms: dizziness on standing after lying down can indicate dehydration or electrolyte depletion. Increasing fluids, salt, and potassium usually resolves it.

Constipation and hydration: dehydration makes constipation worse. Increasing fluid intake is the first intervention for constipation alongside other measures.

Fluid intake: baseline needs increase with gastrointestinal effects and exercise. Thirst is not a reliable guide during appetite suppression. Drinking regularly (not just when thirsty) is prudent.

Sodium: losing weight involves losing some sodium. Electrolyte drinks or salty foods help maintain sodium balance. Very low sodium intake on these compounds raises orthostatic symptoms risk.

I read post #8 twice before replying, because I had assumed the opposite.

Potassium: similar to sodium; losing weight involves some potassium loss. Bananas, sweet potatoes, and other potassium-rich foods help. Severe depletion is rare but symptomatic (weakness, palpitations).

The very ordinary causes of week-two malaise: inadequate hydration, low sodium intake, too-rapid calorie deficit, and inadequate sleep are more common causes of fatigue and malaise than compound toxicity.

post #11 is right about the mechanism and I think understates the practical bit.

Exercise and electrolyte losses: sweating during exercise increases sodium and potassium losses. Electrolyte replacement during or after intense exercise helps maintain balance.

I read post #11 twice before replying, because I had assumed the opposite.

The very ordinary causes of week-two malaise: inadequate hydration, low sodium intake, too-rapid calorie deficit, and inadequate sleep are more common causes of fatigue and malaise than compound toxicity.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.