I don't know where to start. So many things spring to mind for me, because of my own life experience, watching my little brother having the sudden onset of bi-polar syndrome. At the time, in the late 70's, he was diagnosed as a paranoid schizophrenic. His 'meltdown' happened over 3 weeks or so, and it was very similar to what is being described in this case.
First, here are a few things I want to point out, in response to Adreeda's well thought out post, above.
She said:
Few more things which I didn't realise before I started digging and jumped into bandwagon of "mental breakdown"...
Of course, some kind of drug could be involved, as well as actual mental breakdown - it's possible but are odds really pointing into that?
I didn't found any source quotting Sandra Mittank saying that she believes that some mental illnes suddenly appear, she's frequently saying that she believes in that possibility.
But first thing is that people and media are extremely willing to explain any weird event that way, especially if case seems complicated, second - choosing that way is relatively "safe" option as there is no blame pushed into any direction (in this case hotel staff, city of Varna - why there is no footage of Lars from July 7th? "Golden sands" is a very expansive section of Varna, it has to be plenty of cameras, at least at hotels and some on the streets I think, police, doctor) all guilt is put on "mental illness" and people could be more willing to help, third - Lars has no history of mental illness in his family and he never acted strangely before.
Woman from taxi told that had dilated pupils at that time.
There is no information if she was driving to the airport as well, payed for both of them or got out earlier (at least I can't find it).
Dilated pupils could point at drugs but according to the timeline as he catched that ride he spend few hours hiding somewhere in the dark - maybe his pupils were dilated as any other person pupils would be in these circumstances and she assumed drugs because as they reached her it was already stated that he acted weird and runned into the woods frantically? Or she was just nervous because of the situation and as he was scared she assumed that he's nervous because of drugs?
As to the bolded above, our family had no previous history of mental illness, and my brother had no previous mental illness type of incidents. he was in his early 20's at the time. And that is why it took a few months for us to actually realize what was happening to him.
Also, dilated pupils are also a symptom of mania or schizophrenia. It may or may not indicate drug usage.
My brother lived in Bear Valley, where he was a professionals racer. DownHill Racer. He had spent the summer in Chile, outside Santiago, training with the US ski team. He was hoping to qualify for the team.
He lived with his girlfriend. My parents lived a few hours away in the Bay Area.
He called my mom a few times, and sounded strange. he asked her in hushed tones, if anyone had come to her home, looking for him. She said NO, and he said, if they do, don't tell them where I am and don't answer any questions. Then he'd hang up, and not answer her return calls.
There were no cell phones back then, so it was hard to reach him. I tried to call him at his girlfriends, finally reached her and she was confused by him as well. She thought he was hiding something from her, like a new girlfriend, and was upset with him. They had dated since high school, so she knew him well. But even she misread what was really going on with him at the time.
One night he arrived at our parents home, very late. My Mom woke up and found him looking through things in the garage. He had boxes stored there snd said he needed his birth certificate. But he wouldn't say why. But he seemed very desperate to find it.
The next morning I flew up North to talk to him because my Mom was really concerned about him. He would not answer any of her questions and seemed very nervous. She asked me to try and find out what was going on with him.
He took me into the very back part of our yard, and told me a scary but believable story. he said his gf's ex boyfriend was after him. He had been jumped by him and his friends a week earlier, and they threatened to harm him and his family. He said he couldn't tell me anymore for my own safety. But that they were crazy dangerous and he needed to lay low for awhile.
I thought he was speaking the truth. But I also wondered if he had maybe gotten involved with some coke dealers. A lot of ski racers lived the high life back then. So I thought that might be what was up.
The whole thing would take too long to describe, but it devolved into a story very similar to what has been described in the above timeline. He would not drive his own car because he thought it was 'bugged.' So he had me driving him around. And he would be seeing things out of the corner of his eyes, thinking the school crossing guard was watching him, or the lady standing behind us in the store, was following us. And I began to realize that he was either really high, or he was having a mental breakdown.
He went missing the next day. We had no idea where he went because he left a note saying he was going back to Bear Valley. But I knew he wasn't because that is where he said his 'enemies' were. But my Mom wanted to believe that is where he went.
I flew back home. My brother drove up to the mountains and looked all over for him. No one had seen him. So he went to the local Police department and reported him missing. A day or so later, my mom got a call from LE. They found out that he had used the emergency Master Card my Mom had given him.
He had flown to Honolulu. The police contacted LE over there. Eventually they located him. He was found, bruised and battered, on a mountain trail. No ID, No wallet, no money. No idea how he got there, or why he was beaten up. He was in a local hospital and had not given them his name. He had no prints in the system so they did not know who he was. And he would not tell them anything.
When my older brother arrived, my brother thought it was NOT his actual big brother. He was convinced it was the CIA, trying to trick him into going with them. It was very sad. They had to drug him heavily for him to be convinced by his older brother, who he was always very close to, to come home with him.
So the story in this thread seems kind of familiar to me.
How many of those facts have been verified by others besides Lars? Do we know there was really a fight?
Do we know if any doctors really did ask him to sign papers because he might die if he flew?
Do we know there was really a perforated ear drum? And if so, do we know if he might have accidentally harmed himself?
My brother used to get very frustrated by the voices in his head. He tried many odd ways to get it to stop. He once had earmuffs on with tin foil around them, hoping to stop the voices from getting into his head.
My brother had been looking for his birth certificate, I found out later, because he was no longer believing he was really born into our family. he thought we were all CIA and trying to get into his mind and turn him into a robot.
I just hope he's safe somewhere. 
