Exegesis:

anastas apo tēs proseuchēs lit. ‘after rising from prayer,’ i.e. either ‘from the position of prayer’ (cf. v. 41), or ‘from the act of prayer,’ i.e., ‘after the prayer,’ taking apo in a temporal sense. The latter is preferable.

elthōn pros tous mathētas ‘after going to the disciples,’ without connective between anastas and elthōn because the latter denotes an act which is, as it were, part of the event to which the main verb heuren refers.

heuren koimōmenous autous apo tēs lupēs ‘he found them sleeping because of their grief.’ The article tēs should be noted and is best understood as possessive.

koimaomai ‘to sleep,’ here equivalent to katheudō (v. 46).

Translation:

He … found them sleeping, or, ‘perceived (or, saw, or, became aware) that they were sleeping’; cf. on 7.10.

For sorrow, or, ‘worn out (or, overwhelmed) by grief’ (cf. New English Bible, Tae’ 1933), “so great was their grief” (Good News Translation), ‘because they were very sad.’

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.