Showering can cost somebody with ME/CFS two days in bed

ME/CFS has no test, and its symptoms are **common in many other
illnesses** — so the diagnosis is made from a specific combination. **Three
core symptoms are required, plus at least one of two others.**

Required: less ability to do things, with fatigue

A much lower ability to do activities they could do before, lasting **six
months or longer**. The fatigue:

• Can be severe
• Is not caused by unusually difficult activity
• Is not relieved by sleep or rest

The last two are what separate it from ordinary exhaustion. It did not follow
an exertion, and resting does not fix it.

Required: worse symptoms after activity

Post-exertional malaise — symptoms worsen **after any activity, physical or
mental**, that would not have been a problem before.

PEM can lead to a cycle of "pushing" to do more, followed by "crashing."

A crash can bring **difficulty thinking, problems sleeping, sore throat,
headaches, dizziness or severe tiredness**, and **may take days, weeks or
longer to recover from.**

The examples in the source are worth reading exactly as written, because they
say what a day costs:

• Attending a school event may leave someone house-bound for days
• Grocery shopping may require a nap in the car before driving home
• Showering may leave someone bed-bound for days
• Working may mean spending nights and weekends recovering

This is the symptom that makes the illness what it is, and the one most easily
mistaken for deconditioning. Ordinary tiredness improves with activity. This
gets worse, hours or days later.

Required: sleep that does not work

**People with ME/CFS may not feel better or less tired even after a full
night's sleep**, and some have trouble falling or staying asleep.

And at least one of these two

Memory and thinking problems. Most people with ME/CFS have trouble
thinking quickly, remembering things and paying attention to detail — the
state they call "brain fog", being "stuck in a fog" and unable to think
clearly.

Problems being upright. Symptoms get worse standing or sitting up —
orthostatic intolerance. They may be lightheaded, dizzy, weak or faint,
with vision changes such as blurring or seeing spots.

Why the symptoms seem to move

Symptoms are unpredictable and may change or come and go over time.

Which makes the illness hard to describe to anyone, including a doctor: on the
day of an appointment, a person may be able to do the thing that will cost them
the following week.

Source: Centers for Disease Control and Prevention.