Yes, you do.
(Unless, you have oily skin, in which case you do not need a different night cream, so you can watch a panda video instead of reading on.)
BUT ... if your concerns include dry skin, very sensitive skin or are anti-aging, there are some very good reasons why you should use separate day & night creams.
Night creams are much richer. And for a very good reason. A buttery, unctuous Night Cream, applied to clean skin has hours to penetrate, undisturbed. Rich in moisture, antioxidants and skin building blocks, a good Night Cream should provide all the elements for skin reconstruction and plumping. It's deeper hydration also has the power to reduce sensitivity during the day. (If you sleep with air-con on or a heater, a super-rich Night Cream is non-negotiable)
Day creams need to be lighter. Their primary purpose is to protect the skin against the elements (wind/air-con/heat/cold). Their other purpose it to provide a smooth, plumped appearance. Once applied they need to penetrate quickly, for smooth makeup application. They also need to be light so that you don't appear greasy.
Is there a way that I can use my Day Cream at Night?
In a pinch, yes, you can. BUT here is the next BIG BUT ... To use your day cream at night, you should use at least twice as much as in the morning (to provide adequate building blocks for restoration). Which means that your day cream is going to run out really fast. (which makes having both a Day & Night Cream, seem like much better value)
A really good night cream allows you to multi-task and treat your skin while you sleep.
I do love multi-tasking.
So, I guess a good night cream is key to a really good night!