Just copied this from another MN thread discussing Ukraine, from someone who says they are a Russian political analyst:
Despite the very vague threatening statements made by the Russians over the last few days, the US government was reporting a few hours ago that no change to Russian nuclear force posture had been detected. There's no evidence - so far - that this was more than a desperate attempt to retrieve some credibility in the face of Russia's weakness in Ukraine and inability to stop Western states coordinating diplomatic and economic responses.
Even if Putin is mentally unstable - and there's no consensus on that - the people around him, including the senior military leadership, aren't.