I Have Had Some Dizzy Spells Whilst I Am Walking,

I have had some dizzy spells whilst I am walking, and tend to stumble to my left. this has happened on and off for about two yrs ie 6 months in between mentiond it to my GP and he didn't seem real concerned and said I needed to come whilst having them. the dizziness only last for approx 20 to 30 seconds. Today it happened during a game of lawn bowls when I was sitting down, and when the dizziness had mostly subsided, I got up to walk and was undteady on my feet. Felt a little nauseous afterwards and tired, but continued playing bowls. That was approx 3 hrs ago. I am now home,feeling ok other than a bit dull across my forehead!!