CBD can facilitate serotonergic signaling after it desensitizes 5HT1A autoreceptors. Although it shouldn't be a permanent crash - at least I haven't met any case claiming so.
Cannabis, on the other hand, is very risky for PSSD and I've seen several patients crash from smoking cannabis. One of those patients recovered after a full year after a cannabis-induced crash. CBD shouldn't cause this on its own, though, as the crashes from cannabis likely involve long-term depression (LTD) of neural signaling, which mean neuroplastic changes, and are mediated mainly through THC.
down.