In a situation such as the Earth is due to experience, where the majority of bodies will die suddenly leaving the formerly incarnated souls without opportunities, chaos can and does ensue. Crowded incarnations are very temporary.
For instance during the forthcoming pole shift this potential may exist for several months. The normal procedure where immature souls are gathered upon death of their body and amused or otherwise occupied until the next incarnation can be arranged is difficult due to the numbers, so at times these souls are chaotic and roam about and try to arrange their own incarnations.
One of several outcomes may happen:
The incarnation can become crowded. It can occur that multiple souls are incarnating in a body at once, and in these situations all are weak or they would not tolerate cohabitation either.
A fight for the body ensues, where the stronger spirit pushes out all others. Normally the birthing guides prevent such takeovers but during chaotic conditions, this can pass notice temporarily. If the originally incarnating soul does not want to be removed and lingers about in resentment, the birthing guides soon arrive to set things right again.
The takeover spirits are rebuffed from the beginning and no crowded incarnation ensues. This is most often the case, as the originally incarnating soul most definitely has the advantage, being familiar with the territory for instance. The incarnating soul and its human body sense what they might term ghosts or spirits about, and even be aware of spiritual discussions or invitations, but are otherwise not disturbed by the drama which in truth does not begin.