BEIRUT -- The early-morning barrage against rebel-held areas around the Syrian capital immediately seemed different this time: The rockets made a strange, whistling noise.
Seconds after one hit near his home west of Damascus, Qusai Zakarya says, he couldn't breathe, and he desperately punched himself in the chest to get air.
Meanwhile, in rebel-held areas east of Damascus, hundreds of suffocating, twitching victims flooded into makeshift hospitals after a similar rocket barrage. Others were later found dead in their homes, towels still on their faces from their last moments trying to protect themselves.
In interviews after the suspected poison-gas attack Aug. 21, witnesses, survivors and doctors described scenes of horror that they say will haunt them forever.
Activists and the group Doctors Without Borders say at least 355 people died in the attack that has provoked international condemnation and shocked a world largely numb to the carnage of Syria's civil war, which has killed more than 100,000 people in 21/2 years. Fueling the outrage were online videos that showed scores of children killed in the attack.
The rocket assaults came around the same time in two suburbs on opposite sides of the capital: Moadamiyeh to the west and several districts to the east, including Zamalka, Ein Tarma and Arbeen. The two areas are around 10 miles apart.
Ammar, 30, a resident who declined to give his full name and who said he miraculously survived the barrage on Moadamiyeh, said he was awakened by shelling around 5 a.m., just before dawn prayers, when he heard a screeching sound unlike any he had heard before, followed by the sound of people screaming on Rawda street below his apartment. Once outside, he said, he saw a gas with a faint green color. It "stung my eyes like needles."
"I ran out to see what was going on and saw people in various stages of suffocation and convulsions. I tried to help, but then my legs buckled, and I fell to the ground," he said.
Ammar woke up at a makeshift hospital, previously a Red Crescent center, where he said he spent five days getting water, oxygen and injections of atropine, which can counteract the effects of nerve gases. A week later, he said, he has not fully recovered. He suffers bouts of cold sweats, exhaustion, hallucinations and a runny nose. Worst of all, he said, were the nightmares.
"I can't sleep anymore. I keep seeing the people who died, the scenes from the hospital of people twitching and foaming. I can never forget that," said Ammar, who worked in the clothing business before the war and now is a government foe who sometimes deals with the media.
His father, who identified himself by his nickname, Abu Ammar (in Arabic, "Father of Ammar"), was at the nearby al-Rawda mosque along with a small group awaiting dawn prayers when the first rockets hit. He said some people ran outside and then immediately came back in, shouting, "Chemicals! Chemicals!"
He put water on a tissue and covered his mouth and nose, then went out. "I saw at least seven people lying on their backs, completely still," he said.
Mr. Zakarya said the rockets crashed with a strange whistle, "like a siren."
Friends took him to the hospital, where he saw dozens crowding the rooms and corridors, many in their underwear, as nurses and doctors doused them with water. That was when he fainted.
When he came to, doctors were injecting him with atropine, and he started vomiting.