What you describe as a amoeba shaped spot in your vision field is probably an aura symptom of migraine.
Visual migraine aura symptoms can appear in different forms, and the one you have is known as scotoma (an area or island of loss or impairment of visual acuity surrounded by a field of normal or relatively well-preserved vision.)
Migraine aura can be manifested with visual, motor or sensory disturbances, gradually developing over 5 to 20 minutes and generally last fewer than 60 minutes.
The headache phase of the migraine attack usually begins within 60 minutes of the end of the aura phase.
Dizziness is accompanying symptom of migraine.
Migraine headache usually lasts between 4 and 72 hours, and can be triggered and made worse with physical activity.
See a neurologist!