Anytime, I eat oil based foods I fall sick.

What could be the cause?

I mean Groundnut, etc.

I have something similar to this. I feel dizzy whenever I eat something oily or fried, my eyes feels really heavy.
Though I've had gastritis in the past.
I just eat very little quantity of any thing fried or oily.

While im not a doctor and would have left the doctors talk on this but here is my opinion on it. Regardless, of whatever nutrient comes out of fat and oil, it is always important to maintain a balanced cholesterol level, there may be a correlation between hereditary (health issues) and cholesterol related health issues such as heart and kidney issue.

I ADVISE:
1) You reduce the intake of oil drastically in whatever form either in junk or meal;

2) You use olive oil (even when this oil is put in fridge it does not turn solid although very expensive) COMPLETELY;

3) If for whatever reason you can't use olive oil I suggest you use only oil that has the heart sign on it and stated "ZERO cholesterol). You can use popular brand like Power Oil, Mamador, Kings Oil etc;

4) Take supplement that help in the metabolism of fat and oil in the body. (The doctors and health officers on NL could recommend.

5) Visit a lab for sugar level, cholesterol level (if that is how it is identified) and heart to check if there is ANY underlying health issues (that is terminal related).

6) Drink a lot of water (it's never too much)

7) Eat vegetables

I always experience this, especially when I eat yam and fried egg, I will just developed kind of malaria and feverish, and very week.

now I use palmoil to cook every food, jollof fried egg, stew, etc ,

astonished:
I always experience this, especially when I eat yam and fried egg, I will just developed kind of malaria and feverish, and very week.
now I use palmoil to cook every food, jollof fried egg, stew, etc ,

Yeah, I don't think the proper response is to switch to using higher saturated fat for everything you eat. It is probably best you go see a doctor to find out what the problem is, and if it is a symptom of a potentially bigger problem.