If it is causing you to snore and you haven't done so before taking it, then it could be a mild allergic reaction causing your throat to swell or close up.

Citalopram is not know for causing drowsiness but some people may react to medication differently than others.

If you experience any of the following serious side effects, stop taking citalopram and call your doctor immediately or seek emergency medical treatment:

an allergic reaction (difficulty breathing; closing of the throat, hives; swelling of the lips, tongue, or face)
an irregular heartbeat or pulse
low blood pressure (dizziness, weakness)
high blood pressure (severe headache, blurred vision)
chills or fever.


If you experience any of the following less serious side effects, continue taking citalopram and talk to your doctor:

headache, tremor, nervousness, or anxiety;
nausea, diarrhea, dry mouth, or changes in appetite or weight;
sleepiness or insomnia; or
decreased sex drive, impotence, or difficulty having an orgasm.


Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

Everyone reacts to drugs differently...I hated it when I was on it. It also makes you infertile ( read that in the side-effects )

http://www.netdoctor.co.uk/medicines/100000520.html

If you check here, it states one of the side effects of Citalopram is sleepiness although i wouldnt expect it to make you as tired as you describe.. have you read the leaflet enclosed in the pack, they usually give you a list of side effects. Ive taken these tablets in the past but i had the opposite problem, i couldnt sleep or slept very little! Otherwise speak to your doc, he will be best able to help you.

its a bit strange that its making you tired, because its supposed to be an uplifting drug!