you need to use a 2 part self level compound (latex & powder) and mix it with floor granno, difficult to gauge how much you will need without knowing the floor area but any flooring wholesaler will tell you if you take your floor area to them. this should give you the lift you need to bring the floors to the same level and drying times are very quick compared to laying concrete. good luck.
god! sorry just read your post again, i thought it read 5cm :shock: feeling a bit dumb now because it would cost a fortune to raise 5 inches with granno screed mix, possibly again depending on areas it might be worth thinking about digging out the peak and then floating the whole area, could be a lot cheaper.
only other option is to leave well alone, lay you laminate on both levels and get a fancy nosing for the breakline.