The hashtag "why do people get sleepy on high-speed rail" has sparked heated discussion among netizens.
有网友实测发现高铁车厢内二氧化碳浓度较高，认为可能存在因浓度超标导致乘客出现缺氧或犯困症状。
Some passengers conducted their own experiments and found that the concentration of carbon dioxide inside high-speed rail carriages appeared to be relatively high. They speculated that this might lead to symptoms of oxygen deficiency or drowsiness among passengers due to excessive carbon dioxide levels.
对此，12306官方客服下场辟谣：列车行驶过程中会实时更换空气，提供氧气，不会出现缺氧情况。
相关客服还指出，之所以检测二氧化碳浓度变高可能与当天乘客密度变高有关。
In response, the official customer service of 12306 issued a clarification, explaining that during the train's operation fresh air is continuously supplied and oxygen is provided. These efforts ensure that passengers do not experience oxygen deprivation. The customer service also pointed out that the detected rise in carbon dioxide levels might simply be related to higher passenger density on certain trips.
High-speed trains are equipped with their own respiratory systems. The onboard air conditioning systems not only draw in fresh air from outside but also recirculate cabin air to ensure a comfortable travel experience for passengers.
Moreover, the air conditioning systems feature an automatic temperature control function. Temperature sensors installed inside the carriages collect real-time data, allowing the system to accurately adjust the airflow temperature based on preset values. Typically, the temperature inside the train is maintained between 22 and 26 degrees Celsius.
图源：中国铁路
所以，即使在密闭的高铁列车上，车内空气也能保持清新流动，体感适宜，不会出现缺氧情况。
As a result, even though high-speed trains are relatively enclosed spaces, the air inside remains fresh and well-circulated, with no risk of oxygen shortage.
对于一上高铁就容易犯困的原因，网友们忍不住脑洞大开。
有调侃会不会是“白噪音催眠法”：车轮的规律滚动声+空调低鸣，简直是天然ASMR（Autonomous Sensory Meridian Response，意为“自发性知觉经络反应”），让人秒入梦乡。
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