"And being in anguish, he prayed more earnestly, and his sweat was like drops of blood falling to the ground" (Luke 22:44). This had to be startling observation to his disciples, while watching him pray in the garden prior to his arrest. Almost certainly, it was something they had never seen before. Hematidrosis (sweaty blood) is a verified, rarely observed phenomena. It occurs too rarely to be well understood by medical professionals.
Skin biopsy in a hematidrosis case reported in 2008 described small blood collections forming in the dermis (an underlayer of the skin), then evacuating directly through the skin or through hair follicles. In that case report, blood did not directly arise from sweat glands, something that could only be discerned by microscopic evaluation of a biopsy sample. In that case report, the hematidrosis episodes were not connected with threat of harm or religious thinking. The episodes of hematidrosis ceased with treatment for anxiety in that patient. It is not known whether this pathomechanism applies to all case of hematidrosis.
Psychogenic (fear induced) hematidrosis has been observed in a handful of reported cases from fear of impending physical harm. Most of these reported cases were in individuals just prior to execution. This appears to have been the case with Jesus, due to premonition of impending crucifixion (Matt 20:18-19).
It is unlikely that Jesus lost a significant amount of blood by hematidrosis, but it does speak to his mental condition that night. This unusual state of high anxiety would have added to his exhaustion. He would likely have been sweating profusely at times through the night contributing to dehydration, thereby increasing his susceptibility to shock.