PTSD (post traumatic stress disorder) is not a panic disorder. PTSD is characterized by having recollections of the traumatic event (nightmares and flashbacks), avoidance of anything that reminds you of the trauma, and hypervigilance. Panic disorder is different, as it is characterized by panic attacks that are episodic and seem to occur randomly.
However, if you have PTSD and are having a flashback and you are hypervigilant, then it can feel like and look like a panic attack as seen in panic disorder. In PTSD, when you are being reminded of the trauma in your head, then this can trigger a panic attack, characterized by shortness of breath, racing heart, pounding chest, sweating, lump in the throat, and butterflies in the stomach.
