The Deleriants SWIF has used are as follows in order of most intense to least:
Cyclizine
Dimenhydrinate (very structually similar to Diphenhydramine)
Prochlorperazine
Cyclizine is more in the head than Dimenhydrinate, SWIF found him commonly believing things were there as you can see above more so with cyclizine. It is notable that when Intravenous Cyclizine is administered there is a massive pleasurable rush present that is not there with oral administration. This also causes a 5 minute rush of visuals that can be quite intense and unnerving.
All in all SWIF would say Cyclizine is about 1.5 times as potent in effects as Dimenhydrinate both taken at significantly higher doses than clincal.
It should also noted that SWIF is not sure of all the negative effects that cyclizine may have on ones body when taken at above clinical dosages so therefore one should be very careful.