If it is only a head cold, you probably won't do yourself too much damage by going out. But if it is a different viral infection (like flu, or any of the thousands of others) you could make yourself sicker.
Symptoms of a more severe viral infection(and possible secondary bacterial infection) can include fever, muscle and/or joint aches, yellow or green mucous (AKA snot) or sputum (AKA lung biccies), fatigue and more. If you have these type of symptoms, see a Dr, then go home to bed. No-one should be going out with these sort of symptoms. And if you are that sick, the infection will spread very easily to others in a closed environment like a club.