Something that nobody seems to have touched upon is the fact that many dead people are embalmed.

If you suddenly came alive again after being embalmed, you’d suddenly become dead again.

Also, post-mortem examinations are not uncommon if the cause of death was not clear. Again this might lead to instant re-death.

Finally, if the cause of death /was/ clear (such as trauma), then again, that may likely result in instant re-death.