troubleshooting a database that keeps locking up

I have a database that has started to constantly hang after a brief period of activity

looking at `select * from pg_stat_activity;` I roughly see the following each time:

    process 1 | <IDLE>
    process 2 | <IDLE> in transaction
    process 3 | <IDLE> in transaction
    process 4 | <IDLE>
    process 5 | <IDLE>
    process 6 | <IDLE>
    process 7 | INSERT INTO table_a ........  RETURNING id

occasionally I'll see

    process 8 | UPDATE table_b

Does anyone have tips on how I can troubleshoot this.

I was hoping there would be some way to show the history of the "<IDLE> in transaction" processes, but I couldn't find
them.

I was also wondering if the "RETURNING id" might have something to do with this.

I'd appreciate any pointers in trying to figure out what is causing this.