The last two mornings when I get to my computer on my wireless network, I have only the Cisco window visible and no internet access. I look at my Mac settings and another named (not mine) wireless network is shown. I switch it back to mine (which is on the list) and I can get online. It is going to this other network on its own.
I also notice that I have an unstable and weak signal in my living room. The router and model are upstairs. I can get a signal extender but I wonder if the neighbor whose wireless network seems to overtake my own each night has such a strong signal near my downstairs area, that this interference is key.
I would recommend two things before going down the extender route:
1. Change the wireless channel on your router. You don't say what wireless router you have so I can't be more specific. In general, most routers default to channel 6, try 1 or 11. Some routers are smarter and try to find a channel with little to no traffic. It all depends on what you have.
2. On your Mac: Apple -> Location -> Network Preferences..., select your Wi-Fi adapter and press the Advanced... button. On the Wi-Fi tab, remove all but your network from the Preferred Networks list. Press OK. Check the option Ask to join new networks and press Apply.