There are a number of symptoms of low testosterone. Some of which include fatigue, insomnia, hot flashes, hair loss, erectile dysfunction, low sex drive, moodiness, increased body fat, and more.  Additionally, lower testosterone scores often lead to drops in bone density. This means that bones become more fragile and increasingly prone to breaks.  However, someone with a lower score still may not show any symptoms.  That being said, even if a man does not show any symptoms, he may be well advised to seek treatment.