Hello, I have gone through your query and understand your concern. There are numerous causes for Excessive fatigue, tiredness and sleepiness. It is very usual after a prolonged work in night shifts and frequent shift changing. Frequent shift changing and night shift usually alters our Circadian rhythm. Circadian rhythm is nothing but a our body s own physiologic and biologic clock. Blood pressure can be low in night shift workers and frequent shift changers due the disturbance in circadian rhythm. Some common medical condition you have rule out are Anemia and Hypothyroidism and Diabetes. Have a healthy life style, eat in time , exercise regularly, try relaxation techniques like yoga and meditation, Spend enough time with your good friends. Plan and do the work so that you can not get frustrated or depressed. If still the tiredness and sleepiness is more, then you should consult a general physician and further investigation may be needed for the diseases which i mentioned earlier like blood check, thyroid hormone, blood sugar etc. Hope this helps. Please write back for further queries. Wishing you good health.