Blizzard have issued a statement regarding the recent EU server lag and their efforts to fix it. It seems while they did try to address it, the fixes did not work (yet), so you should be very careful when playing Hardcore on EU realms this weekend. These issues are not affecting all players, however, but even a mild lag could be the difference between life and death. 

Lag (Source)

Hi all,

Just a quick update before we head into the weekend:

While we initially saw some improvements following last nights work and restarts, things appear to have become progressively worse again and troubleshooting continues.

In terms of in-game messaging it is being considered, though keep in mind not everyone is affected and a generic message about potentially running into issues is already true at all times. Having warnings appear and disappear might simply create unrealistic expectations about when it is and isn’t “safe” to play.

As for rolling back or reviving dead characters we’ve tried our best to be as clear as possible from the very start that it’s not something we will consider, which remains the case.

I understand losing characters to any technical issue is disappointing, but for purpose of keeping this thread useful for the ongoing work to address the issue, please try to keep the discussion to currently experienced symptoms – and thank you to those already contributing with this info!

Stay safe for now and hopefully the underlying issue can be finally addressed soon!