While on horseback, changes in vertical viewing direction are dampened, similar to F8 mode (though not as pronounced), causing them to lag behind mouse movement. As this is uncommon for Minecraft in particular and ego games in general (not to mention that it is inconsistent with horizontal mouse response) it can lead to motion sickness (rangin from an unspecific feeling of discomfort to dizziness and possibly nausea and headaches) even for experienced gamers, and shound therefore be avoided.