I bought my grave a few weeks ago, and I can tell you- going to your spouse's funeral is the closest thing to attending your own.
You are so close to that person- sharing one life, one flesh- sharing a past, a future- that seeing their body there- the one that you know every mark on, every freckle, every scar, feels very much like seeing your own- and it feels that impossible and that horrifying.
So, although each grief and loss is different- I don't believe any death will force you into your own mortality as much as a spouse's death. For that is you up there- that is your life as you knew it, and that is your grave beside his- where others will stand and lower you in.