There are a few possible reasons that your Sim wont sleep in their bed. The likeliest reason is that there is a stereo or television within earshot that is keeping them awake. If your sims have different schedules it is possible that the insomniac Sim is being kept awake while your normal Sim watches TV. Later, when the roles are switched, your insomniac Sim is doing something else so your normal Sim is able to nap. Because of this it appears that your insomniac Sim is afraid of that specific room when it's really external circumstances that keep them awake.
Alternatively - and assuming your Sims are in a relationship, your bed could be positioned in such a manner that your normal Sim is able to climb into bed on one side whereas your insomniac Sim could not reach the bed from the other side. This would have to mean your Sims are consistently sleeping on "their" same side of the bed to replicate this issue. Unlikely, but not impossible. Try moving the bed to a different part of the room.
Lastly, your game might just be bugged. From what I know and what I've researched there is not a mechanic which causes a Sim to be "scared" of a specific bed. It seems to be external factors. If those factors can be ruled out then you may have to update or uninstall and reinstall your game. Other uses have said travelling or moving into a new house and then moving back fixed a similar issue. YMMV
You can read about other players attempts to troubleshoot on EA forums