Hi i am Dr Ahmed Aly thanks for using healthcaremagic site , I had gone through your question and understand your concerns .. I think that could be a sign of anemia or weakness as you mentioned . this could vanish simultaneously without medical treatment with bed rest , morning exercises and some B12 multivitamin supplementation . If this issue became more frequent i suggest you measure your blood pressure and have some lab investigation for proper evaluation and management of underlying cause . Please click and consider a 5 star rating with some positive feedback if the information was helpful. Wish you good health, Any further clarifications feel free to ask.