Your coils are shot... You have a few choices...
1) oem nissan coils (ref number: 55020M, about 110$ USD Each)
2) OME aftermarket coils which will give you about .75 inch higher stand than if your coils were oem new : OM922 about 75$USD :
http://ruggedrocksoffroad.com/pathfinde ... 8_593.html
3) Automotive Customizer custom coils which gives you 2" of lift...not recommend if you do not lift the front too...: about 90 $USD each :
https://www.4x4parts.com/catalog/produc ... ts_id=2303
to change them you will need a floor jack, 2 stands and a good set of sockets and air impact or electric impact. About 1 or 2 hours total.
This is common of the r50, your front too will eventually sag and will need to be replaced..usually at around 80000 kms..
S.