Ask yourself if you’re still getting a good night’s sleep on your mattress, or if it still looks like it’s in good condition. A mattress that’s sagging or has permanent indentations likely means the bed has lost its support. If you continue to sleep on it, you may find yourself waking up with a bad back. Other signs that the mattress is losing its shape include lumps and rips. Before you buy a new mattress, you might want to double-check your warranty. Most manufacturers will replace a sagging mattress, but how much the mattress needs to sag to qualify for a replacement varies. If you find yourself getting a full night’s sleep (which for most adults is 7 to 9 hours) and still wake up tired, it may mean that your mattress is no longer comfortable and supportive enough to help you recover while you rest. And if you wake up and find yourself sneezing or feeling congested, the culprit might be allergens that have built up in your mattress over the years.