Tang Hebe first noticed something was amiss from the moment when she saw Cui Xukun appear all of a sudden. She was truly taken aback to see him but Shui Xian didn't look surprised. Also, the moment that Shui Xian called her 'Tang Hebe' instead of 'Bebe', made her feel unsettled.
It was this uneasy feeling that made her keenly observe everything around her. And doing so, she managed to find the date that left her startled. She had to check the tv to figure out if the date was wrong but something told her, the date was right. Eventually, she was proven right.
To be very honest, when she first realized that she lost her memories, she was not only feeling lost. She felt very scared as well.
