Sleep is vital to our everyday function. However, the National Sleep Foundation reports that lack of sleep is affecting a large number of Americans. In fact, 35 percent of respondents to the National Sleep Foundation Sleep Index Poll cited their sleep quality as poor. In many cases, a mattress may be to blame. Don’t sacrifice sleep. Here are four signs that it’s time to swap your mattress. You Wake Up Achy or Tired Think it’s time to replace your mattress? First, analyze your sleep. If you are having trouble getting a full night’s rest or waking up achy and tired,…