Hi there, thank you for taking the time to review your Serta Morning Slumber Medium Mattress. Your feedback is valuable to us. We are sorry to hear about your experience. If your mattress is sinking or sagging in the middle, it may have a manufacturing defect. If that is the case, we encourage you to reach out to your retailer to begin the warranty claim process. If approved, you may qualify for a replacement mattress, which should help give you the wonderful nights of sleep that you deserve. If you would like to share more with us, feel free to reach out to our team directly through the contact us page on our website with any questions, comments, or concerns.