Jeffrey Ghazarian died Thursday morning at a Pasadena hospital after spending 5 days hooked up to a ventilator and battling for his life ... according to his family.

His sister says ... "He suffered a lot and put up a good fight. We will miss our Jeff everyday but we are thankful for all the fun happy memories of the times we had together."

Jeff's timeline regarding his COVID-19 infection is terrifying and should be eye-opening for people of all ages. According to his family, he flew from L.A. to Orlando on March 2 for a work conference, but stayed a few extra days to visit Disney World and Universal theme parks with friends.

We're told on March 7 he developed a cough, and the next day he coughed up blood. He flew back to LAX on March 9 ... and immediately went to the ER, where he also had a high fever.

The family says a chest x-ray confirmed Jeff had pneumonia, and he was tested for COVID-19 and sent home with fluids and antibiotics and instructed to self-quarantine until he got the results back.

We're told the results came back positive on March 13, and Jeff was provided a portable oxygen meter to keep an eye on his levels ... which took a turn for the worse that afternoon.

On March 14 he was taken by ambulance to the hospital and quickly transferred to the ICU when it was discovered his lungs were 60-70 percent blocked with pneumonia. Doctors decided the best path forward was to sedate and intubate, hoping a ventilator would help his lungs heal.

Sadly -- and despite the family claiming he was approved for antiviral meds -- the medication was delayed in getting to him, he took a turn for the worse ... and passed away Thursday morning.

It appears Jeffrey was higher-risk patient. He had a history of asthma and frequent bronchitis as a child, though he outgrew that. He also had undergone surgery for testicular cancer back in 2016.

The CDC now says young people can also be at grave risk ... and this underscores the danger.

He was 34.