Re-order Paragraphs

Put the sentences in the correct order:

1. ▲▼Understanding these stages has therefore reshaped how doctors think about everything from memory to long-term brain health.
2. ▲▼Researchers believe this nightly cleaning helps explain why a single sleepless night leaves people foggy and forgetful.
3. ▲▼One of these stages, known as deep slow-wave sleep, appears to be when the brain clears out metabolic waste that builds up while we are awake.
4. ▲▼Modern recordings of brain activity, however, show that it cycles through several distinct and highly active stages each night.
5. ▲▼Sleep was long treated as a passive state in which the brain simply switched off to rest.