Could I be low in something?

[Bathsheba]

Hmm, dizziness can be a circulation problem, you say you are drinking enough water, that's really important. You haven't been ill lately? I wouldn't want to frighten you but have you had glandular fever or any other serious virus recently? Y'know if it continues for more than a few days i'd just go to your GP and request a blood test. Your electrolytes could be unbalanced too maybe?

ETA: found this:

All higher lifeforms require a subtle and complex electrolyte balance between the intracellular and extracellular milieu. In particular, the maintenance of precise osmotic gradients of electrolytes is important. Such gradients affect and regulate the hydration of the body, blood pH, and are critical for nerve and muscle function. Both muscle tissue and neurons are considered electric tissues of the body. Muscles and neurons are activated by electrolyte activity between the extracellular fluid or interstitial fluid, and intracellular fluid. Electrolytes may enter or leave the cell membrane through specialized protein structures embedded in the plasma membrane called ion channels. For example, muscle contraction is dependent upon the presence of calcium (Ca2+), sodium (Na+), and potassium (K+). Without sufficient levels of these key electrolytes, muscle weakness or severe muscle contractions may occur.

Any unbalance can be detected via blood test.