When I sing, I get dizzy, If I focus hard I feel some kind of numbness in my hands and around my forehead. This happens especially when I sit down while singing. Am I making too much effort while singing? What could be causing this?
First of all, these are symptoms that should always be checked with a doctor. They might show up first in circumstances creating exertion, such as singing, and indicate something more serious.
If there is any relationship between these symptoms and singing, it would be because you are over-breathing, taking in too much air when you inhale, crowding the lungs and causing yourself to hyperventilate. Then, when you sing, there might be excess breath pressure driving into the head resonators. It can generate an exciting tonal quality for a short time but very soon becomes debilitating. If changing your breath eliminates it, great. If not, see a doctor.