SUSPENDED generally means the process is waiting on something that is not being done by MSSQL. For instance, if a long running process is waiting for the operating system to return something being read from disk and it take awhile, the process may be suspended while SQL waits for the operating system. Since the process is not under the control of the SQL server, it suspends the process until whatever it is waiting for is done.

I have seen this come up a few times while TempDB is expanding or a huge query is trying to pull a lot of data from a busy disk drive.

I also seem to remember this happening sometimes with linked servers waiting for the remote server to process something, but that part of my memory seems to be a bit fuzzy right now.