What is the difference between decongestants and antihistamine in treating cold?

Why take one during the day and the anti histamine at night? Is it because the antihistamines knock you out?

I thought that a medicine with antihistimine was to help the person with sleep when they have a fully blown cold. I remember this chickadee in the chemist told me that the difference in the day/night tablets was the night tablet contained an antihistimine to help with sleep. Obviously a decongestant is just that. It decongests the phelgm and helps loosen it. Maybe this chickadee was also just feeding me a whole lot of hooha.

Decongestants will dry nasal and chest mucus. Antihistamines work well for allergy symptoms to block the histamine response which can help stuffiness, sneezing and other allergy type symptoms. For congestion, a decongestant is needed. If your congestion is allergy related you may need both antihistamine and decongestant. If you have a cold, you want a decongestant. If you also have a lot of sneezing and eyes itching etc you may want to add an antihistamine as well. Antihistamines are often added to cold medicines for the side effect of drowsiness so you can rest as much as or more than their ability to work on congestion.

decongestants tend to unblock your nose and chest, it depends or how clogged you feel. An antihistamine is supposed to block or slow the release of histamine, which produces the excess mucus. If your nose is running and you are sneezing, you may can get by with just an antihistamine. Now if you are like me and woke up sneezing your head off, but your lungs and nasal passages are still clogged, you need to take the decongestant too. I have already had a claritin redi-tab, some fluticasone nasal spray ( rx) and a walgreen's brand guaifenesin/psuedoephedrine today, just waiting for them to work.