100 mm seems very excessive, but I don't think the amount a bike sags under its own weight is relevant. It only matters how much it sags with rider weight. The amount the bike will sag under its own weight would vary with the spring you have installed. With the bike properly set up for a heavier rider, the bike wouldn't sag under its own weight as much as a bike properly set up for a lighter rider.
Again, I don't think that the amount a bike sags under its own weight is relevant, but unless it's sprung for a toddler I wouldn't think it would sag 100mm.