These symptoms are present in a wide variety of medical conditions. The possibilities include dehydration to lack of sleep. Pay attention to what other symptoms and signs you may be having. Adding more symptoms and signs may help better pinpoint what may be going on. Try to drink plenty of fluids and get some rest. If your dizziness or symptom of feeling faint get worse, seek care urgently. For any symptoms and signs that concern you or don't go away, your doctor is your best resource to help you get to the bottom of what's causing them.
While the list below can be considered as a guide to educate yourself about these conditions, this is not a substitute for a diagnosis from a health care provider. There are many other medical conditions that also can be associated with your symptoms and signs. Here are a number of those from MedicineNet:
Dehydration is the excessive loss of body water. There are a number of causes of dehydration including heat exposure, prolonged vigorous exercise, and some diseases of the gastrointestinal tract. Symptoms of dehydration include headache, lightheadedness, constipation, and bad breath. Treatment for dehydration is to replace lost fluids and electrolytes.
When sleepiness interferes with daily routines and activities, or reduces the ability to function, it is called "problem sleepiness." A person can have problem sleepiness without realizing it. Symptoms of problem sleepiness include: consistently don't get enough sleep, or poor quality sleep, fall asleep while driving, struggle to stay awake when inactive (like watching TV or reading), have difficulty paying attention or concentrating at work, school, or home, have poor performance problems at work or school, have difficulty remembering things, have slowed responses, have difficulty controlling your emotions, and/or if you have to take naps on most days.