Is it safe to mix Dayquil and Nyquil?

I have both dayquil and nyquil, but the ones that are specifically for coughing. Both have the same amount of cough medicine, but the nyquil also has an antihistamine. I want the antihistamine effects for my allergies, but i don't want a full dose because it makes me pretty drowsy. But I need a full dose of cough medicine to treat my coughing. So is there any problem with mixing half a dose of dayquil with half of nyquil? Thanks.