I feel a quick instance of dizziness then i feel shortness of breath and really sleepy. what can it be. it happens out of no where ?

Arrythmia: Many things could cause this but dizziness and shortness of breath could come from irregular heart beats or heart rythms. In many situations if this is the case you will feel palpitations. It would be important to check for history of heart murmurs, thyroid function levels, nutrition, hydration etc. Start with simple things. Good eating and sleeping habits. Exercise. See how you feel