Oh no, crOOk buddy, I'm sorry to hear you had such a bad time, at least it sounds like you're OK now and no harm was done.
Know that we've all done stupid things, even if we're more knowledgeable than the average drug user. I myself came very close to death one time when I was at university. After finishing exams I mixed a few too many 10mg valiums with a lot of alcohol. I never mixed benzos with alcohol again since, and have since treated benzos with a lot more respect, only keeping them for emergencies. I'm sure your experience will teach you to be more careful in the future because you sound like a generally responsible adult. These are potent mind-bending drugs we're using and they have the potential to make a fool out of anyone.
On a lighter note, I was not aware of diphenidine having serotonergic activity. I'm beginning to wonder are there *any* receptors that are safe from this drug? Seems like quite a broad binding profile.
I wonder why your lithium level was high, could it be that you didn't take it twice, but some protein that metabolises it was saturated by the other drugs you took? I know nothing about the metabolism and excretion of lithium but it sounds like a possibility.
Also, can you please compare diphenidine and 2-MeO-diphenidine for us? I'm very curious to know.
EDIT: Reading your post again, I had another theory.
Sorry for the constant wild speculation, but this is a harm-reduction site and I think it's important to discuss the details of your bad experience as much as possible here. Others might benefit from it.
If indeed diphenidine has serotonergic activity, and since you had taken venlafaxine which is an SSRI, and lithium which increases serotonin synthesis, is it not possible that you might have had a serotonin syndrome? Do you think the symptoms you experienced matched
those of serotonin syndrome? Again, in my stupid years I once took a fluoxetine that someone gave me and somehow thought it would be fun to mix it with some L-tryptophan, my theory at the time being that more serotonin = better high. After a very strong headache, sweating and overheating I think I may have slept for days although to this day I'm not exactly sure what happened. I was a know-it-all idiot and I got punished for it.