Feeling Weak and Shaky within minutes of eating?

Today I felt weak and shaky only 5 minutes after eating a slice of fruit cake. I'd eaten it earlier today also without the shakes and I've had plenty of protein too.

All of a sudden I felt like I didnt have any strength and that I needed to lay down or I would collapse and faint. Lasted around 10 minutes or so and then slowly the feeling went away.

Is this anxiety or does anyone think this is actually related to food? I have been diagnosed with two different anxiety disorders (OCD and PTSD). I recently had a blood test which showed normal blood glucose and everything else was perfectly normal. Also blood pressure is normal. I've been suffering with an inner ear infection for 9 months and the doctor took a blood test recently, showing nothing wrong with me in terms of my blood. However he doesnt know what is wrong with me but I believe it to be uncompensated labyrinthitis as Ive had all the symptoms now for months.

If it helps.. I also feel constantly fatigued, I wake up not feeling refreshed and if I do any exercise I start to feel weak and tired after a short period of time.. which is not normal for me as Im only a 24 year old guy who has never had anything like this in my life before.