I suddenly lost balance, what is happening?

Well, im 17 years old and though im not proud of it, i had started smoking 6 months ago, however i have gone from about a pack and a half a day to 2 cigs a day but yesterday evening i was at work and it was kinda hot in there and i felt a little dizzy but nothing to dramatic but than i went to my church for a youth group meeting and we were hanging out playin some extreme pingpong which involves a bit of running around and i was weariong a jacket and I think i may have over heated and than i was leaving cause i wasnt feeling to well, and when i went to look out the church window i all of a sudden lost all sence of balance and like evreything was spinning and it lasted about 5-10 seconds and went away so i took my jacket off and sat down for a while and left, so when i got home i was feeling okay and about 2 hours later i was sitting on my bed watching tv and it happpneded again and i almost fell out of my bed (i was sitting up) uhmmm i dont have any pain in my head or anything and i hadnt slept well the night before and was really tired the whole day idk if it was the combination of heat and exhaustion or if something is seriously wrong and right now i kinda feel dizzy, what do you guys think cause i havent had an episode of loss of balance yet this morning im thinking if it happens again to go to the doctor.