Sounds like a lack of oxygen, he was very busy 43 and did Berlin a lot, as well as others, I do hope this opens up a whole new world to you about your father, a brave man.
2/3 December 1943 - Berlin
2.12.43 17 aircraft detailed for tonight’s operations, the target being Berlin. One aircraft was withdrawn, another P/O Billing and crew returned early, the captain having collapsed but recovered sufficiently to land back at base. The remaining aircraft raided the target in quarter moon – 7/10ths cloud top 5,000’ – vis good. Defences H/F predicted moderate, about 200 S/Ls around the city forming cones when cloud breaks permitted. Many fighter flares and activity. TIs fairly well concentrated and many incendiary bombs and bombs burst in area. Later the markers appeared to be scattered. Reports vary considerably, some saw no fires, others saw fires and much smoke in three columns to 10,000’. No good concentration was maintained and results are difficult to assess. S/L Garlick DFC B Flight Commander and his crew failed to return. No news has since been received. The remaining 14 aircraft returned safely to base in the early hours of the morning. F/L Riches’ aircraft was peppered by flak, the pilot himself having a knock on the head which rendered him unconscious – on coming to, the aircraft was in a vertical dive but he managed to bring it under control.
JA908N P/O J.B.Billing, Sgts T.W.Hope, J.E.Moriarty, P/O E.E.Osler, Sgt J.M.Campbell, F/Sgt R.D.Curtis, F/Sgt J.B.Findlay. Up 1710 Down 1835. Sortie abandoned owing to captain fainting at 13,000’.