Not always. Clear, watery drainage is often just allergies. But some signs are worth having checked, rather than ignored.
See a doctor if the fluid only comes from one side, tastes salty in the back of your throat, gets worse when you lean forward, or if you've had a head injury or sinus surgery before.
If any of this sounds like you, a simple lab test can check the fluid, and a scan can find where it's coming from. Don't guess on your own — but don't ignore it either.