Etymology- i need a reminder word for hypo- and eu-, and -err-?

I don't know about the other, but regarding hypo and hyper I simply think of hyperactive. I know that hyperactive means you're getting excited and *over*ly active. Therefore hyper means over and hypo (the opposite) means under. Or I think of hypoglycemic which means your blood sugar is low (I'm around several diabetics). Hyper(active) has always been the key for me.