How Can dizziness And Headache Along With Rapid Heart Rate Be Treated?

I have been very ill with what I thought was gastro but have now been in bed 4 days and can only crawl to the toilet . When I stand I get dizzy and very breathless and my temprature makes me sweat , headache and very fast heartbeat . Been drinking plenty of water and have a fan on me but feel after four days besides the fact I am not throwing up or going to do number two all the time I m not improving . The first day I had this my feces was very dark and I have had anemia before and they have done a thorough search of my small and large intestine which was clear at the time . I just want to be able to get on with life and feel well ,what s your thoughts ?