Too much nitrous oxide can cause symptoms that vary in severity. These symptoms often include physical and neurological signs, such as dizziness, weakness in the legs, loss of balance, hypoxia, and numbness in the limbs. Long-term exposure to nitrous oxide could cause vitamin B12 deficiency.Too much nitrous oxide can cause symptoms that vary in severity. These symptoms often include physical and neurological signs, such as dizziness, weakness in the legs, loss of balance, hypoxia, and numbness in the limbs. Long-term exposure to nitrous oxide could cause vitamin B12 deficiency.