Wreaths are displayed along the Freedom Wall at the World War II Memorial. (Marvin Joseph/The Washington Post)

J. Mark Jackson served in the 82nd Airborne Division and the 101st Airborne Division in the war in Afghanistan in 2009.

Thank you for your service. Veterans are grateful for these words. But for the combat veteran, there is an unspoken, inaudible phrase that follows: And for your continuing sacrifice.

The experience of war, of direct combat, is trauma. It leaves a psychological residue on each veteran; call it mental plaque. Veterans carry this as baggage throughout their lives. The mental trauma experienced determines the level of encumbering psychological residue. It is a sliding scale, but at some point along the continuum, it reaches beyond mental baggage and enters the horrific and debilitating realm of post-traumatic stress disorder. But make no mistake, all combat veterans carry a lasting, indelible imprint of the horror of war.

The condition is persistent. I have met Vietnam War veterans who get chills talking about their experiences even now. I have seen World War II veterans — American, British, German — become choked with emotion discussing their wartime experience as much as 60 years later. This residue of war is no modern phenomenon: It is universal and timeless. It is a dark gift that keeps giving for the lifetime of the veteran.

For this combat veteran, it means:

• Carrying the knowledge, always, that I killed or was a party to the killing of other humans, regardless of their status as the enemy.

• Feeling an almost out-of-body experience when a pair of fighter jets fly over. I am mentally transported back to a desperate fight when the jets flew in so low that the afterburners burned my gunner's neck. I shiver as I return to reality, although the temperature is above 90 degrees.

• Admitting that I cannot watch war movies any longer. They make me too uncomfortable.

• Dreaming I am back in the war zone. In my dreams, it always looks different, but I always wake up agitated and disquieted just the same.

• Rolling out of bed aching and broken from "military wear and tear," knowing that the Department of Veterans Affairs will never acknowledge my pain.

• Suggesting my son play motorsport or fantasy video games. The sound and the realism of the military games make me edgy.

• Avoiding large crowds because I cannot trust my behavior if I am pressed too closely.

• Finding, in quiet moments, that images and memories of war creep back, at first in tableau but moving rapidly to the forefront of my mind. Sometimes I must physically shake my head to clear the thoughts.

• Realizing that I am, at some part of my core, a violent person capable of startling acts. This realization humbles and frightens me.

• Feeling my eyes well when I discuss some emotionally powerful events from the war, no matter how many times I have mentioned them before. Eventually, I stopped talking about them to avoid the reaction.

• Living my days having prepared for death, accepted that fact and then survived anyway. This changes the fabric of your existence for the rest of your life.

• Dreading the Fourth of July fireworks because they sound so much like a mortar attack.

• Discovering I no longer want to hunt or fire guns, although I did both most of my life.

• Restraining myself from registering my disgust whenever a non-veteran informs me how a war really ought to be fought.

• Seeing a sunrise for what it is: a splendid gift I should not still be alive to witness.

Writing this was cathartic. I hope reading it is, as well. Please continue showing your gratitude to the veterans you meet. It means much to have our service acknowledged and appreciated. And remember that when you thank combat veterans for their service, you bestow recognition for demons they willingly shoulder for us all.