Diphen vs Doxy
My $.02:
Diphenhydramine HCL (Benadryl) is a far better *antihistamine*. Doxylamine succinate (Unisom) frankly sucks for runny noses. If your nose is running, or you are sneezing, Diphenhydramine is the best (non non-sedating antihistamine) hands down, use it, it is much better at stopping a runny nose than Doxy at any dosage. 50mg is a good starting dosage, 100mg being the maximum.
Also, diphenhydramine HCL (Benadryl) is a decent sedative and has a moderate half-life. In other words, it is good if I need a quick knockout punch and know I won't get more than 5 or 6 hours of sleep. Even at a higher dosage (75-100mg) it seems to wear off quickly and leave me reasonably ready to go in the morning. But, it's not as strong as doxy, which in some cases (only 5-6 hours of sleep available) is a good thing.
Doxylamine succinate is a better sedative but has a long half life. Overall it knocks me out better and keeps me asleep better but can leave me feeling groggy in the morning at any dosage. If I know I can sleep in (8+ hours), I will choose the Doxy every time. 25-50mg. Be forewarned when shopping for doxy. Read the label. I usually look for the generic version of Unisom that has just the doxylamine succinate in it, usually 25mg per tablet. Typically 1 tablet (25mg) is about the right dosage. I have no problem going up to 50mg but, again, the long half life WILL leave you groggy feeling in the morning. At the 50mg level expect 10 hours of total "grogginess."
In terms of mixing, it is fine but just don't over do it. I'd say max for me (180lbs) is 50mg doxy and 100mg diphen max. I will usually start off less than than and max out at that. My days of drug abuse are over. At some point in my life I learned to respect drugs, stop abusing them, and use them to improve my life. Anyway, if I can't sleep in (8+ hours) I don't mix them at any level.
Both of these are sedating drugs. If you have allergy problems during the day I would recommend going with something non-sedating (loratadine aka Claritin) or mix in 60mg of the REAL pseudoephedrine HCL (aka Sudafed BTC behind the counter lol) with your 50mg of diphenhydramine hcl. The Sudafed "PE" aka new formulation aka the stuff available over the counter now is total junk and plain does not work. I've battled stuffy noses my whole life and the government replacing pseudoephedrine hcl with phenylephrine has to be the dumbest thing I've seen in the US OTC market. But I digress...
I find Ambien, Ambien CR, even the 12.5mg level to be completely useless. But I have been taking low dose diazepam (aka Valium 10mg/day) for years now. I can stop at any time for weeks with no issue yet it still helps me relax in crowded places and slows my generally always racing mind. I find clonazepam extremely sedating at 1mg+ and not that good at controlling my anxiety. I find diazepam sedating at 15mg+. I typically don't use benzos or non-benzos for sleep though. I get prescribed 10mg/day of diazepam for anxiety. I take 5mg in the morning and 5mg before bed. Works good for me as I have a generalized anxiety disorder. In the benzo world I found clonazepam to be better at sedation and diazepam better for anxiety. Xanax is far too powerful/addicting and Ativan (lorazepam) is fast but weak. But benzos are an entirely different discussion
Take care and titrate up slowly. Don't do stupid stuff like sniff diphenhydramine or take 800mg of it. Be safe, respect drugs, they will respect you and improve your life. I've been down the bad road, take my advice and respect them.