Consistent with the info on depression of the respiratory center in the brain, I found this info some time ago. The study showed how hypothyroidism affected regional cerebral blood flow to specific areas of the brain.
http://jnm.snmjournals.org/content/45/10/1712.abstract
"Arterial blood analysis indicated a frequent incidence of hypoxia in hypothyroidism. The incidence of hypoxia was 69%. The hypoxia was improved by thyroxine replacement therapy. In 6 patients examined for the ventilatory control, all had the index for hypercapnic ventilatory drive lower than normal control. It was suggested that the hypoxia in hypothyroidism was caused by a depression of the respiratory center in the brain and by anemia."
Excerpt from "Unusual manifestations in primary hypothyroidism" Yamamoto K, Saito K, Takai T, Yoshida S. PMID: 6222384 [PubMed - indexed for MEDLINE]
I'm not sure it is directly associated. What thyroid disease do you have?