Please advise how to show what posttraumatic stress disorder (ptsd) feels like?

IT DEPENDS: Your question suggests that somebody does not believe you. I would start by telling such a person what ptsd is and what might cause it. You do not need to be specific about what your traumatic event was. I would then tell the person to suggest to me what he/she imagines it would feel if s/he had been traumatized. People experience ptsd very differently but no matter how it does it hurts.

Might not be able to: You may not be able to. I don't encourage combat ptsd patients to try to explain war or all of their sxs to spouses. Why? Because the spouses usually don't have the experiences to base an understanding for it. Inevitably the person with ptsd feels misunderstood or badly about the upset it has caused the other . This is why it is so important to work with a therapist who is experienced with ptsd.

PTSD: Ptsd can follow any traumatic event, depending on relevance of event to the person. Anxiety with intrusive recollections & avoidance become evident.

"Show" or "know"?: Most ptsd sufferers alternate between hypervigilance and fear from re-experiencing trauma (including nightmares), or numbing and avoidance of situations that resemble the traumatizing experiences or could be triggers for this. Either is painful. Sometimes it helps to write or draw, or to move the body vigorously. Meet regularly with a group of others who do know what it feels like. Therapy works.

Symptom inquiry: The doctor should inquire if the patient has been in a situation where the patient believes loss of life or catastrophic injury was imminent, and with no means of escape. Symptoms from these experiences include, hypervigilance, sleep loss, nightmares, reliving the trauma, social withdrawal, anhedonia, temper outbursts, emotional withdrawal, feelings of unfinished business, and adrenalin seeking.