While In Work Today I Went Outside For A Break,

While in work today I went outside for a break, stood up to go back in side and I felt dazed and lost my balance, collapsing back down to the chair. I stood up again, felt good enough to work so I continued my shift until 11:30. I have now a mark on my forehead that has appeared today. Can you suggest what I should do? or what has happened to me please?