There are no nested interrupts, except that a high priority interrupt can interrupt a low.
Repeated interrupts of the same type will only set the interrupt flag for that type. If the flag hasn't been cleared, it's lost.
Ex: You have the interrupt enabled on low-to-high transition of an RB0 pin. Button is pressed, RB0 interrupt flag is set, which causes the code to hault and enter the ISR. Your ISR checks all the flags and finds RB0 flag is set. This has taken a number of clock cycles, and the button has bounced which keeps causing the RB0 interrupt. Well, it's only reasserting the fact that the flag is 1. Your ISR code will eventually assign 0 to the flag and return to the main code.