I dunno, It could go either way, but I agree, let's be consistent. It all depends on how we want to look at it, if the message is a result of the attack, then it would be past tense, since the message is describing what happened. But the message could also be stating what the new status is, so present tense applies. Personally, I am a fan of the past tense version, so that the message is a commentary of the attack, and not a voice of god telling me what is going on.
For the slow issue, I would say Medion became weary or Medion is weary, I never liked how games used "slowed". Even tired works better.