EMB ERJ 145 ER/LR
Situational Awareness; Physiological - Other; Communication Breakdown
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Illness / Injury
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Human Factors; Procedure
During cruise flight; I noticed the Captain grab the oxygen mask and use it to breath. He then turned the air temperature way down. Afterwards he told me that he was feeling dizzy and light headed like he was going to be ill. He said he was having trouble staying focused. We continued our descent as he said he was feeling better after the oxygen. He said he was still not 100 Percent. I noticed that he was having a little difficulty reading back the instructions but that he was okay and good to continue. The Captain was the Pilot Monitoring and I; First Officer; was the Pilot Flying. We were given a descent via clearance.... I then set 6000 as the bottom hard altitude to follow the Vertical Path Indicator down. Initially we were given the 8L transition; which was the assigned runway via the arrival. We were then given a frequency change to another Controller and what I heard him say was change runway 8R and fly present heading. I heard the Captain read that back. Since I did not hear anything about an altitude; I assumed that we would continue to our last assigned of descent via or 6000. We leveled off at 6000 on present heading and the Controller asked 'Say altitude.' It was at that point we were made aware of a possible pilot deviation. I asked the Captain if he had heard an assigned altitude and he said he thinks it was 8000. Supposedly; the ATC Controller gave us fly present heading; maintain 8000; and switch runway to 8R. I never heard the 8000 and never changed the altitude selector to 8000. It was left at 6000. The pilot monitoring never said anything about an altitude that I recall. If I had been aware of the 8000 restriction; I would have set 8000 in the altitude alert. I'm not sure if I got mixed up with the 8R and 8000 or if someone stepped on the last part of the transmission and I never heard it. The Captain said afterwards that he remembered the ATC Controller saying 8000 but he never mentioned to me to change my 6000 to 8000 as a level off. The Captain at that particular moment was still a bit out of it from his sudden sickness which may or may not have played a part in a breakdown of monitor cross check.
EMB-145 First Officer reported an altitude overshoot during descent while the Captain was not feeling well.