Older "2.5D" game engines (like vanilla Doom and the BUILD engine) use a number of tricks to simulate a three-dimensional scene that can be disorienting, especially when your player-character is looking up or down, crouching, leaning, or otherwise not looking directly straight.

Modern engines like GZDoom or eDuke32 have full-fledged 3D renderers, rather than the quasi-3D renderers of old. If you don't get motion sickness playing modern games, then playing Doom on an engine with a modern renderer might be helpful.