to have something happen in (my, in this example) time; or, for something to happen to me (see Molina)
Orthographic Variants:
nopan mochihua, nopam mochiua
Alonso de Molina:
nopam mochiua. (pret. nopan omochiuh.) acontecer algo en mi tiempo, o acaecerme algo. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 73v. col. 1. Thanks to Joe Campbell for providing the transcription.