There are many medical complications associated with #eatingdisorders but not everyone "feels" them. Some people do; for example, dizziness upon standing (or seeing "black spots" ) can be contributed to orthostatic changes in blood pressure and heart rate (due to gravitational shifts when changing position from lying to standing) as well as bradycardia (low heart rate) and/or hypotension (low blow blood pressure).
You can have all of these complications and never even know! You can also have a life-threatening low potassium level from vomiting, laxatives or diuretic use, and also not "feel" it. Some may say they "feel fine." If there are medical parameters indicating that your body is not functioning well, it could be that you are just not paying close enough attention, or that you lived this way for so long you don't know what "feeling better" feels like?
There are also very serious cases where there are no obvious medical abnormalities (yet). You may go to the doctor and "things look good." for now. This doesn't mean you are not damaging your body. Some bodies just respond respond differently. Over time, eating disorders cause a variety of issues that effect many different body systems. The harm caused from the eating disorder, both physically and emotionally, cannot be underestimated.