Ustadh, is it allowed to pray maghrib and isha together if you cant stay awaka that long?

If one day you are going through something where, for example, you haven't slept for a whole day (24 hours or more), or if you are sick and extremely tired, and on that specific occasion you know you need to sleep and cannot wait for Isha: You can pray them together. You can combine the prayers, pray, and then sleep.