Fruits cause a crash but processed sugar doesn't.

15 grams of sugar from fruits will cause an immediate crash where I feel extreme fatigue within 10 minutes and all my muscles freeze up. [I've tested this so far with both Apples, Watermelon and Sweet Corn].

But interesting if I consume 15 grams of sugar[sucrose] from a chocolate bar I feel fine which doesn't make any sense considering fruits are lower GI and have no chemical additives compared to a chocolate bar I find this extremely strange.

The only different I can see is that fruits have direct fructose whilst the chocolate bar contains sucrose but doesn't this break down into fructose anyway?