lightheadedness since one week.. whats wrong?

It started last week and since then has come back every day, mostly after 4 p.m., but also once or twice during morning/afternoon, especially after walking around or just doing exacting physical or mental work. Sometimes it lasted one hour, sometimes until i went to bed.

those are the SYMPTOMS: feeling weak/exhausted and lightheaded. Kind of like i was tipsy/a bit drunk without having touched alcohol. Im dizzy but not like vertigo, where everything spinns around me, or when you get up to fast and feel weird. it's more like everything is dulled, my senses are slower, my field of vision is limited (not like tunnelvision thoug, its rather a problem of focus maybe). Also i was less concentrated, (very) few times even lost track of what i was saying. When walking i felt weak on my legs, even with fear of falling at some points... Also sometimes i got light headaches.

What could it be? Since it occurred i have paid special attention to drinking enough, eating balanced meals (except for meat) I have a lack of iron () and b12 (), but could this effect in such symptoms so suddenly? Also exactely one day before it started, I had a minor medical intervention where i was given propofol which made me sleep for 30-60 mins. Afterwards i was a bit drowsy and tired for the day, but else totally fine. could it have to do something with that?

I have already arranged a meeting with my GP, but in the meantime I wanted to ask here aswell....