What could cause a feeling of disorientation and inability to concentrate very well?

Many things. Many things can cause feelings of disorientation and inability to concentrate. Consider any kind of drug intoxication or withdrawal -- same for alcohol. Various kinds of infectious encephalopathies either in CNS or from outside it. Stroke. Metabolic encephalopathies like severe hyperglycemia, liver or kidney failure, severe hypothyroidism, wernicke's, etc. Head trauma. Brain tumor. Others.