One, the ongoing aggression against the Ukraine
Two, the rivalry with China.
Well, right now China is taking over Philippine territory and threatening Japan, Vietnam, and India, so it is only a matter of time until they try to get Vladivostok back.
China also has the worse pollution, labor force, corruption and stability problems than the West, or even Russia. Failure to cope with these problems may do more to hobble Chinese growth than anything the rest of the world does about growing Chinese economic and military power. Both of these items terrifies Russia because Chinese economic power is a growing presence in and around Russia and China has ancient territorial claims on the Russian Far East.
Third item: Saudis overpumped oil to keep the price down, to hit Iran's economy, but also affected other countries like Russia (not to mention the Texas economy). If Russia will help them in Syria, they will slow down and force up the price of oil...
but fracking complicates this.
As I said: For later reading.
another article on background here notes Russia aims to rebuild their military but lacks money.