‘Sleeping sickness’ is caused by

Sleeping sickness, also known as Human African Trypanosomiasis (HAT), is a potentially life-threatening infectious disease caused by protozoan parasites of the genus Trypanosoma [2]. Specifically, the disease is caused by two subspecies: Trypanosoma brucei gambiense, which accounts for over 90% of cases, and Trypanosoma brucei rhodesiense [1]. These parasites are transmitted to humans through the bite of an infected tsetse fly (genus Glossina), which is endemic to sub-Saharan Africa [2]. The parasites eventually migrate to the central nervous system, leading to the characteristic sleep disturbances that give the disease its name [3]. In contrast, Plasmodium species cause malaria, and Leishmania species cause leishmaniasis. Paramecium is a free-living ciliate protozoan and is not a human pathogen.

Sources

1. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC7562814/
2. [1] https://www.ncbi.nlm.nih.gov/books/NBK535413/
3. [3] https://www.cdc.gov/dpdx/trypanosomiasisafrican/index.html