Sudden weakness and tiredness can be caused by various factors, including:

• Hypoglycemia (low blood sugar)
• Low blood pressure
• Dehydration
• Medication side effects
• Sleep disorders or lack of sleep
• Stress, anxiety, or mental health conditions
• Nutritional deficiencies such as low iron or vitamin D
• Chronic medical conditions like heart disease, diabetes, fibromyalgia, or chronic fatigue syndrome
• Infections or illnesses (e.g., flu, urinary tract infection)
• Lifestyle factors such as poor diet, too much or too little exercise, or excessive caffeine intake

If the sudden weakness and tiredness are persistent, unexplained, or severe, it is important to see a healthcare provider for a proper diagnosis and treatment plan as it may signal an underlying health condition.