<grinning> For some reassurance (or for a total freakout) check out a copy of the PDR (physicians desk reference), or go online to drugs.com and just start looking at different meds.
EVERY single med on the planet has about 50 possible side effects. The top 5-10 or so are listed for every medication (meaning that they cause those effects in at least 2% of the population). Even tylenol has a "scary" list of possible side effects. Check out the list of side effects for birthcontrol pills (stroke, heart attack, cancer, blood clots). As a matter of fact one of my sisters becomes deathly ill with tylenol. Doesn't mean it's not a safe med, just that she has an adverse reaction to it. Some people react that way to tylenol, but it is less than %0.001 of the population. Maybe a dozen people out of hundreds of millions, or even a billion. It's one of the safest drugs on the market. But even it, still has it's list of side effects.
The reason we have these huge lists is that FDA approved drugs have been, and are continuously, rigorously studied. Most of the scary side effects are essentially our body "rejecting" the med, similar to an allergic reaction (but technically different).
My cousin is an herbal pharmacologist. (MD, Pharmacist, she has more letters after her name than the alphabet). Part of what she's working on is compiling similar lists of reactions and uses for non-fda regulated drugs. Some of the things she's studying are fascinating (antiviral properties of certain native religious ceremonies, etc.), and some are downright scary (things sold over the counter in the "beauty"/ natural section which would NEVER pass an FDA study. Hylands, for example, will NEVER be allowed in my house. I'd allow LSD or magic mushrooms before teething tablets. (I'd use whiskey and sugar before a hallucinogenic nerve toxin).
Anyhow... the list of possible side effects are things *to keep an EYE out for*, not to freak about. Meaning/Example; if a side effect is nightmares, & you notice frequent nightmares, it's not because school started... but probably related to the med, so time to try a new med. Ditto if a side effect is diahreeah, it probably wasn't the chicken chow mein, but the med. Knowing what the side effects of meds are allows us to treat responsibly. My husband drives me NUTS about this. He started an antidepressant a few years ago, and almost instantly broke out in a rash. Instead of linking it to "duh, I just started a new med, maybe they're linked" he decided that we needed new laundry detergent, or that maybe he needed new seat covers. Sigh. Lets see here baby. You started a new medication a week ago. 3 days later you break out in a rash. Ya THINK they might be related?
The mood thing is common to MOST anti-histamines for the very simple reason that MOST antihistamines make us sleepy, and when we're tired we tend to have mood shifts. Some get hyper, some get cranky. So you'll notice in the PDR, that EVERY med that tends to make people sleepy is also listed as possibly affecting mood.
The POSSIBLE side effects aren't worth freaking out over, just keep an eye out for them.