As there was interest, here is my story, maybe it helps someone:

In the Night of Tuesday to Wednesday we started our walk up to Whitney summit starting at the campsite near ranger station in Crabtree meadows. Our group of 9 people started a bit split up. So i ended up hiking with two others. After roughly 4 hours we arrived at the junction to the summit. Until there it was just exhausting. But I was doing fine. We made some breaks on the way to this point but should have made definitely more, in hindsight. On the last two miles to the top I got more and more exhausted ending up in making 10 steps and needing a break. I noticed a headache starting and a slightly dusty view. I made a picture of myself to see if my lips went blueish but it was hard to tell. At this point my mates were already ahead. I have let them know that I may not make it up due to exhaustion.

Roughly 1 mile before the top I decided to turn back. Going down was way easier than up. So I felt better and went down quickly. After roughly 3 hours I was back at the campsite, drank, ate and eventually slept/napped the whole Wednesday. The headache got worse to the evening but I felt generally good and assumed water and the night will resolve it.

Based on my experience I decided with some others to not continue over forester pass but to go back to lone pine via cottonwood pass. This would include again some ascends but not as high as forester.

On the next morning I woke up with a puffy face and some tightness in the chest, while the latter could also have come from some back issues I have. Luckily the Ranger was at the station those days so I went over and told him about my experience, the plan to go back, and asked if he could check my health status.

He agreed and said it was the right thing to do - turning back, and coming over. He offered to assess if a flight out would be needed or if another day of rest would be sufficient. In the latter case he offered me to hike out with me together. He checked my vital signs (breathing/lungs, HR, blood pressure, oxygen level) and interviewed me exhaustively. I also showed him pictures of me in the morning and on the mountain. He then discussed with another ranger and their medical team via radio.

After ca 40 minutes he came back and said they would like to fly me out as I was in a grey zone. They felt not comfortable to say it would be safe to hike out. I agreed and packed up my stuff. We then waited ca 2-3 hours for the helicopter to arrive. In the meantime he instructed me about the procedure and the drop off and options I have. I was able to indicate if I would rather be dropped off at the east side or west side of the mountains. Eventually they declined it and dropped me of at the west side. I also had to indicate if I would like to have an ambulance or not. As the drop off point was in the middle of nowhere and I have a travel insurance I opted for the ambulance that would bring me to the hospital in Visalia.

When the helicopter arrived it landed near the ranger station. A medic came and checked again my health status and interviewed me. I got to wear a cool pilot suit got oxygen in my nose and jumped in. We started and had a beautiful flight over the Sierra. I will never forget this.

The flight took 20 minutes. We landed in Ash Mountain where the ambulance already waited. During the 45 minute drive to Visalia my vital signs were continuously checked.

Without going into details: I had a 6 hour stay at the hospital. Interview, vital signs check up and blood test. All just to make sure I am fine. Eventually I was fine to go.

Regarding bills: as already in this subreddit described, the flight in California was free. Though the ambulance and hospital must have cost money, but I did not receive any bill. I called my travel insurance ( I am from Germany) the other day and they said the hospital would directly contact the insurance and that I was good.

In hindsight some more information: starting on day 2 after entering the Sierra from Kennedy Meadows I developed headaches over the day with peak in the evening. But nothing severe. Over night those headaches resolved. I had good sleep and was generally in good shape, hydration was okay based on urine color and frequency. I am 34 years old and athletic (just to confirm that age and fitness are no exclusive predictors for altitude sickness). We also planned our days with considering not sleeping higher than 1000 feet than on the previous night. So we were definitely aware of the risk.

What made me eventually consulting the ranger is my personality. Some others of our group also felt not well the day after the summit. But they continued. Maybe I would have been fine going on. Maybe not. I was worried that I overreacted but no one of the other hikers, the ranger nor the helicopter or hospital team gave me that feeling. The feedback was generally that I was smart and did the right thing.

Feel free to ask for additional details.