You might be interested in a few answers I've written:

• It's June 1st, 1991. I'm a State Department employee at the Soviet Union desk. What am I thinking about the longevity of the USSR?

• I'm an Estonian officer in the Soviet Navy on a mission at sea in 1991. What happens with me when Estonia declares independence, when USSR acknowledges it, and when USSR finally dissolves?

• Kazakhstan was the last country to leave the USSR. What was it like in the 4 days in which the USSR only existed in Kazakhstan?

I picked out these three in particular because they get at different parts of the question. In short, "was the fall of the USSR a shock?" Yes and no. Starting in 1989 it became clear that Gorbachev's reforms were leading to ever bigger and more drastic changes in Soviet institutions and society. There was no going back to 1985.

But where the USSR was going wasn't really clear until pretty much the dissolution happened (even as late as December 16, 1991, Gorbachev was working as Soviet President theoretically in charge of a Soviet government, even as pretty much all Republics were declaring their independence and the Communist Party of the Soviet Union was already banned).

As for institutional reactions, here are a few:

• When the Soviet Union dissolved, how was the process handled in the UN? In particular, was there a period of time where no one was able to exercise the Soviet/Russian veto on the security council?

• How did Yeltsin gain control of the army/police when dissolving the USSR?

• When the Soviet Union collapsed, what happened to the Communist Party and all their stuff?