Sympathetic Tone

Amygdala

The threat detector. Dense in androgen receptors, and the structure most implicated in the anger, vigilance and fear side of what these compounds do. Splitting it out of the limbic system matters because threat processing and reward processing sit in the same blob otherwise, and compounds pull them in opposite directions.

Resting Heart Rate

Beats per minute at rest. A cheap daily read on sympathetic tone, and usually the first number to move when something is pushing the nervous system.

Anxiety

Restlessness, racing thoughts, a wired feeling. Multiple routes reach it: neurosteroid changes at GABA-A, glucocorticoid signalling, sleep loss and thicker blood.

Insomnia

Difficulty falling or staying asleep, often with night sweats. Its own problem, and an amplifier for every mood effect above it.

Nightmares and Vivid Dreams

Intense, unpleasant, memorable dreams, usually alongside broken sleep and night sweats. Named separately from insomnia because people report it even when total sleep time is normal, and because it is one of the few effects that reliably resolves within days of stopping.

Panic Attacks

Discrete episodes of overwhelming fear with a physical surge: pounding heart, breathlessness, a conviction that something is badly wrong. Different from sustained anxiety and worth its own entry because the plausible route is different too, running through sympathetic tone and a raised resting heart rate rather than through mood.