A sudden and unexplained weight gain can be confusing, especially when your daily dietary pattern and exercises routine have been consistently healthy. And before you look for a solution, you need to identify the source of the problem. Here are four possible conditions your weight gain may be a symptom of:

1. Thyroid disorder

If your thyroid gland does not produce enough hormones, you might have Hashimoto's disease or hypothyroidism. Among the many associated symptoms, unexplained weight gain and low levels of energy are the most common ones.

It can be dangerous to leave this type of condition untreated on a long-term basis. After you are diagnosed, you will be prescribed medication to help compensate for your underactive thyroid. Once you settle into the right dosage, your weight is likely to return to normal.

2. Insomnia 

It is recommended that healthy adults get at least 7 to 9 hours of sleep per night. Most of us know that staying up too late can increase hunger and appetite, eventually leading to those midnight snack cravings. But it may have to do with a lot more than that, according to researchers from Sweden.

In their recent study, just one sleepless night was found to cause changes in the body, promoting a higher storage of fat. This suggested that poor sleep itself could lead to weight gain by "reducing proteins that are the key components of muscle," according to lead author Jonathan Cedernaes.

3. Depression

In many cases, depression might be accompanied by changes in body weight — sometimes, they lose it and sometimes, they gain it.

In the second scenario, it is possible that the depressed individual spends more time in bed and undergoes a gradual decline in physical activity as a result. It is also possible that the person may adopt a food-related coping mechanism to deal with their mood problems, such as eating unhealthy snacks that are high in calories.

Belinda Needham, an assistant professor at the University of Alabama at Birmingham, also points out increased production of the stress hormone cortisol. Experienced as a consequence of mood disorders, higher levels of cortisol could also lead to weight gain.

4. Cushing's disease

"Cushing’s typically presents with significantly low energy and complications like diabetes, high blood pressure, and high cholesterol," said Dr. Reshmi Srinath, assistant professor of diabetes, endocrinology, and bone disease at the Icahn School of Medicine at Mount Sinai.

Excessive weight gain accompanied by red stretch marks around the abdominal area is a strong sign. Srinath also notes how the patient only gain the weight in their middle and the back of their neck, while their arms and legs stay lean. If you are experiencing these signs, it is important to get them checked out by a health professional as soon as possible.