I was reading Yusuf Ali's English translation where he states for translation of Quran 8:11:
"Remember He covered you with a sort of drowsiness, to give you calm as from Himself, and he caused rain to descend on you from heaven, to clean you therewith, to remove from you the stain of Satan, to strengthen your hearts, and to plant your feet firmly therewith."
The aya in Arabic is:
إِذْ يُغَشِّيكُمُ النُّعَاسَ أَمَنَة ً مِنْهُ وَيُنَزِّلُ عَلَيْكُمْ مِنَ السَّمَاءِ مَاء ً لِيُطَهِّرَكُمْ بِهِ وَيُذْهِبَ عَنكُمْ رِجْزَ الشَّيْطَانِ وَلِيَرْبِطَ عَلَى قُلُوبِكُمْ وَيُثَبِّتَ بِهِ الأَقْدَامَ
My Arabic is lacking in finding which word is interpreted to mean "drowsiness".
Picthall's translation reads:
"When He made the slumber fall upon you as a reassurance from him and sent down water from the sky upon you, that thereby He might purify you, and remove from you the fear of Satan, and make strong your hearts and firm (your) feet thereby."
I don't think Allah sbwt made them actually sleep. I interpret this metaphorically as putting the believers in an alternate state of consciousness where they are very relaxed but on a heightened state of alertness; calm but ready and alert with alpha brain waves dominant. This can be achieved with meditation. Athletes try to achieve this state before competition and I am sure it is beneficial for warriors before and during battle. I am speculating because I am not well versed on the sirra and hadiths. Any help appreciated.