Testosterone is a hormone that handles many physical characteristics to males in particular. This is an important role in sexual reproduction and maintenance of bone and muscle mass.
Testosterone levels dropping down very low can affect males in having lower sex drive but more so, left feeling fatigue &/or lethargic.
When there is not enough testosterone circulating in the body, it can mimic other symptoms of various ailments.
A question I had also answered on Quora which has relevance to this post.
Some of the symptoms of androgen deficiency include:
- hot flushes and sweating
- breast development (gynaecomastia)
- increased body fat, particular around the abdomen
- weaker erections & orgasms
- loss of body hair
- increased risk of osteoporosis
In understanding how testosterone affects men will need further research.