> ## Documentation Index
> Fetch the complete documentation index at: https://docs.medera.info/llms.txt
> Use this file to discover all available pages before exploring further.

# Arousal & Regulatory Systems

> arousal · arousal_regulation · circadian_rhythms · sleep_wakefulness

| Construct            | Description                       |
| :------------------- | :-------------------------------- |
| `arousal`            | Physiological activation level    |
| `arousal_regulation` | Autonomic modulation              |
| `circadian_rhythms`  | 24-hour biological rhythm         |
| `sleep_wakefulness`  | Sleep quality + daytime alertness |

Key contributors: facial `stress_index`, `pns_index`, `sns_index`, `hrv_rmssd`, `hrv_lf_hf_ratio`, assessment context (insomnia / sleep items).