\IEEEPARstart{P}{hysical} pain can be defined as the negatively-valenced experience associated with actual or potential tissue damage \cite{loeser2008kyoto}. Pain in neonates is categorized into three main types, acute procedural pain, acute prolonged pain, and chronic pain \cite{anand2007pain}. Acute procedural pain is often caused by a short painful stimulus (e.g., immunization) and it ends as the cause of pain (i.e., stimulus) is removed. The acute prolonged pain (a.k.a., postoperative) is triggered by a clear stimulus (e.g., surgical procedure) and has a clearly definable beginning and expected end point; the intensity of this type of pain decreases as a function of time since the painful stimulus occurred. The third type of pain, chronic
