If you are new and haven't read our website yet, visit templeofzeus.org, and especially look at this link for new initiates.
If you are asking about meditation, start with the 40 days meditation program by High Priest Zevios Metathronos
Read this article from the Library of Thoth.
libraryofthoth.org
This could happen but only in a very isolated case if you take things to the extreme and practice a specific meditation that your body cannot handle (advanced members can provide insight on this).
Rule of thumb: Always follow the instructions on the website. If you go to our meditation section, the levels are organized from beginner, intermediate, to advanced, so follow everything step by step.