Chills, Drowsiness, Lightheadedness, Mild Tachycardia, Nausea In The Mornings With Diarrhea, Per-syncope Symptoms, Normal Blood Tests

I ve been having chills with normal temperature since yesterday evening. I m also feeling a bit drowsy and light headed with sligh tachycardia that comes and goes every now and then; symptoms correlating to hypotension . I m 26 and had an episode of syncope last year and Pre-syncope symptoms yesterday and last week. I ve had blood tests that all came back normal, FBC, U&E, CRP , ESR , TFT, LFT. I also feel nauseated in the morning with diarrhoea but this tends to go away later on in the day and doesn t occur daily. I m a doctor myself and I am really clueless about what other work ups towards a Dx I can do.