Dear you have not mentioned your age sex and any illness such as hypertension diabetes you are diagnosed with..on the basis of information that you have given it seems the case of benign peroxismal positional vertigo.in this condition you will develop dizziness and nausea in a particular position of head and in some other you may feel relatively normal. Is there any history of recent sore throat cough fever ear ache etc.if present this will suggest vestibulitis .apart from this your blood pressure if it is increased can cuasing all this cervical spondylitis can also cause this...Sometimes indigestion also can cause feeling of nausea. If we consider something serious it may be because of some cardiac dysfunction as well..but my first diagnosis will be BPPV that I described you earlier but other causes must be ruled out.in my opinion you should consult your physician for complete history and examination and take his advice for that.hope this will help.