Feeling weak and tired can be caused by a wide range of factors. Common causes include lifestyle issues such as not getting enough sleep, poor diet, lack of exercise, or excessive physical activity. Stress, anxiety, depression, and emotional exhaustion also play a major role in causing fatigue. Additionally, underlying medical conditions like anemia, thyroid problems (hypothyroidism or hyperthyroidism), diabetes, infections, heart disease, chronic fatigue syndrome, and vitamin deficiencies (such as low vitamin D or iron) can lead to persistent tiredness and weakness. Sleep disorders such as sleep apnea or insomnia could also be contributing factors. Sometimes medications or substance use including alcohol and certain drugs cause fatigue as well. If the weakness and tiredness are ongoing, severe, or unexplained, it is important to consult with a healthcare provider for proper diagnosis and treatment, as fatigue may be a symptom of a treatable medical condition.