Generally speaking, although I dreamed of a grave, I didn't feel afraid in my dream. The tomb in that dream should be more a symbol of end and nostalgia than death and disaster. Of course, there may be other symbolic meanings, and this cannot be generalized. "Digging wild onions" is a very special thing, not the usual "digging wild vegetables". Does this feature mean anything to you? And that friend who accompanied you, is there anything special for you or does he have anything in common with someone?
Interpretation of dreams is a personal matter, and it is difficult to make a more specific and targeted interpretation only by simple plots. Just chatting casually.