If you have succeeded in setting up your own business, I very much doubt you are a lazy person. Not being able to motivate yourself to do the smallest of things is very much a symptom of depression (I speak as a sufferer myself). It can be triggered by external events, but often there is no cause at all - a fog just descends and it's as though you can picture yourself doing X thing, but there's an invisible barrier stopping you.
It would be worth speaking to your GP, although the likelihood is that if they diagnose depression it will be a prescription for anti-depressants and a long waiting list for any sort of counselling. If you can fund it yourself, counselling might be worthwhile.
Also think about whether anything is triggering this - or whether there might be some past, unresolved issue or trauma in your life. There might well be nothing at all, but sometimes it can be traced to a kind of delayed reaction to something that's happened in your life.
You say you are happy when your partner is home - have you talked to your partner about this? Sometimes articulating your feelings can help, and your partner may be able to help you devise coping strategies.
If you can find ways to cope and get by, and things to do that make you feel happier, even in the short term, it can help you get through the dark periods.
The worst thing you can do is blame yourself or think of yourself as 'lazy'. Depression is an illness, just like a physical illness, and you need to be forgiving of yourself, or else you will make yourself feel worse.
I hope you can get some RL help and support. 