Everybody gets blocked at one time or another. Sometimes it lasts a few hours, sometimes weeks or months. And the factors that lead to it are limitless: stress, poor health, mental or physical exhaustion, difficulties in personal relationships, or JUST PLAIN RESTLESSNESS. (In which case, do you really need another trip to the refrigerator?)
When you find yourself blocked, try and figure out why. If you're just feeling rundown, take some time to get your mind and body back into working order. Pounding the keyboard when you're knackered is a losing battle. If it's something more, like a creative standstill, there are exercises you can do to get your juices flowing again. And there's no shame in taking breaks.
Writer's block is NOT, however, something we claim when we'd just rather be sleeping or playing whiffle-ball. Don't blame the muse because you have ants in your pants. Get a routine and try to stick to it, even if it hurts.