sesame/nut allergy question

While I know that ILE is not a health-care website, I wanted to ask this question anyway: Does anyone know why I'd be allergic to sesame oil, but apparently not sesame seeds?

Here's the deal: I can eat a sesame-seed bagel or hamburger bun and not think anything of it. However, if I dare eat any amount of tahini, or any other product with sesame oil, I will break into anaphylactic shock and probably need to go to the emergency room. Is it just the concentration of sesame in the oil?

Also, is sesame somehow related to cashews and pistachio nuts, both of which make my throat close up and my stomach hurt?