Ella Swann, 14, was part of Solihull Swimming Club at North Solihull Sports Centre, Birmingham and completed part of the 90-minute session when she was discovered at the bottom of the deep end of the pool.
Ella was rescued and lifeguards gave her first aid as paramedics arrived at the scene to take over treatment.
BirminghamLive reported she was rushed to Birmingham Children's Hospital on February 28, but sadly died in hospital two-days later on March 2.
An inquest held at Birmingham and Solihull Coroner's Court on Tuesday (August 30), heard that Ella had suffered from epilepsy, which was diagnosed at the age of 10.
However, she had never previously had any seizures during physical activity.
Her fits had usually happened early in the morning lasting around two-minutes, but she had not experienced any seizures for two-years and her medication had been reduced.
She then suffered two seizures in January 2022 and her medication was restored by doctors, the hearing was told.
Detective Inspector Jim Edmonds, from West Midlands Police's public protection unit, said there was no CCTV which covers the pool area where the tragic incident took place.
He said all appropriate risk assessments were completed by the sports centre and the swimming club.
Visibility assessments and water checks were in place.
He said head counts were taken every 30-minutes and staff present all had relevant qualifications, including first aid.
Her swim coaches were aware of her epileptic condition, the hearing was told.
Outlining a timeline of events, DI Edmonds said: "At 20.35 the swimmers entered the pool. There was a head count at 20.45 and that determined there were 32 swimmers in the pool.
"We believe at 21.00, the swimmers were at the side following the first set and Ella was present at that point.
"They then did their second set and were called back in."
Ella came back in third place out of six people following a swimming set in lane two, according to her coach Matthew Kelly.
He said the swimmers were in when he looked at his notes for between 10 and 20 seconds before he was alerted that Ella was submerged.
This discussion lasted for between 15 to 20 seconds before Ella was helped out of the pool by another coach and a lifeguard, the hearing was told.
Two lifeguards then started CPR at the poolside.
The hearing was told that it remains unclear exactly how long the teenager was under water as it was an "unwitnessed submerging."
A 999 call was made at 21.05 and paramedics arrived at 21:11.
A defibrillator was used to regain Ella's heartbeat.
She suffered a further cardiac arrest before arriving at the hospital's intensive care unit in a critical condition, the hearing was told.
Giving evidence, Doctor Antonio Pérez-Iranzo, a consultant in paediatric intensive care at Birmingham Children's Hospital, said on the balance of probabilities it was likely that Ella had experienced a seizure while in the pool.
He said: "She was a known epileptic. It is very likely she had some epilepsy activity while she was swimming and that led to her losing consciousness."
The doctor said Ella took on water and suffered a cardiac arrest in the swimming pool.
"One of the difficulties of the resuscitation was the removal of food material (due to vomiting)," Doctor Pérez-Iranzo said. "I think that really complicated the resuscitation.
"During my job usually it's one of the complications while we are trying to maintain the airway of the patient.
"That contributed in a high probability of maintaining a return of circulation of Ella.
"After all the resuscitation she was admitted to BCH. She was very unstable.
"I feel the main issue was this prolonged cardiac arrest with difficult resuscitation. That led to a severe lack of oxygen to the brain.
"The cause of death was related to a hypoxic event based on her epilepsy.
"The CPR was prolonged and complicated with hypoxia due to aspiration of food. That all led to hypoxic-ischemic brain damage."
Senior Coroner Louise Hunt for Birmingham and Solihull confirmed with the doctor that the cause of death was "hypoxic-ischemic brain damage, as a result of drowning, as a result of a generalised chronic seizure while swimming."
A jury sitting during the inquest are due to complete a record of inquest.
They were sent out to deliberate their conclusion before being sent home for the day.
The panel will return today to resume their discussions.