[_98fj]

> What do you mean by "slow"? Hours, days, weeks, months, or years?

Depends on the issue, but yes. Weeks to years.

> Singular use of LSD or other 5ht agonists is unlikely to cause serotonin syndrome in lieu of other metabotropic properties which affect the serotonin system.

Technically correct. Diagnostic criteria include temperature > 38 °C for example, so it's only called serotonine-syndrome when symptoms get into the dangerous zone. What LSD does anyway is steering your body into that direction, so you might not have 38°C on LSD, but e.g. 37.4°C. Simply because it affects serotonergic systems and those regulate body-temperature. I'll update my post.