It was 11:30, so she wasn’t expected that I was sleeping. I tried to hide that I was sleeping. I spoke very clearly and louder than necessary. The trouble was I had to speak in English.
When we met afterward, she asked me if I was sleeping at that time. I had to tell her the truth. She said she noticed that my voice was strange.
We chatted for a while and I realized that it was getting difficult to catch what she said. More than that, I couldn’t follow what I was saying. We finished tea and went home, because it seemed I was losing concentration.
I reconfirmed that the duration of my concentration is two and a half hours.