Ok, well, here's a PubMed article for you and I'll paste the abstract:

https://pubmed.ncbi.nlm.nih.gov/3516567/

"Syncope and other vasovagal reactions occasionally occur at or immediately after IUD insertion. This analysis, using an international data set comprised of interval insertions of Lippes Loop D, found that women who are primiparous (as compared to those who are multiparous), and/or those who want more children are at higher risk for vasovagal reactions and deserve more careful counseling and gentler cervical manipulation. Moderate to severe pelvic pain at insertion is closely associated with the development of vasovagal reaction. Measures to alleviate or prevent pain at insertion could reduce the incidence of vasovagal reactions."

It sure seems to me that providing some measure of pain management would prevent these reactions.