OK - so here's my take on it (which may not generalise for everyone): The experiences I had with Salvia were never bad as such. But on this occasion it did leave me somewhat jumpy and unsettled for a few days afterwards - like someone was watching me even when no one was around (which, depending on your beliefs, you might say was exactly what was happening).
I'm told it lasted under 10 minutes. I couldn't tell form my perspective as I'd just experienced what I thought being outside of time looked like! The after-effects take a while to taper off - so no driving or operating heavy machinery or lighting BBQ's for at least 2 hours.
Before that I'd tried LSD, weed, poppers, and Brugmansia (plus a pretty long list of milder plant-based entheogens) - but had also had some pretty interesting experiences with mediation, sleep deprivation, exhaustion, and lucid/semi-lucid dreaming (though not all at the same time!)