" In Arrest" It probably means he was paroled or captured and made prisoner. Also there were many causes of being sent to the hospital, the most casualties from the war were from other diseases such as dysentery, yellow fever, diarrhea and other poor living conditions.
Dear Samuel McKinney,
Thank you for posting your question on History Hub!
As was mentioned, "In arrest" generally means being "in a state of confinement." for one reason or another. "Debility" was a common term used to describe a general weakness, caused by some diagnosed, or more often undiagnosed malady that affected soldiers in camp or confinement. Disease was the number one killer of troops on both sides and any time soldiers were in camp, diseases like dysentery, typhoid, malaria, etc. were rampant. The National Archives page on Civil War records (https://www.archives.gov/research/military/civil-war ) is a great resource for understanding records from this era. Also, if you haven't done so, check out the Family Search Wiki on Civil War records https://www.familysearch.org/wiki/en/Beginning_United_States_Civil_War_Research .
We hope this information was helpful. Best of luck on your research!