I understand what you are saying as i feel this way very often and hate how i feel at home, i am mentally ok when i have things to do, and going about them no one would think mu mental state was anything but normal or good, but it is like a light switch as soon as i get indoors alone, i can't be bothered to do things even when i have the energy there, feel sad. bored, unhappy, and just want to hibernate away from everyone and everything, really struggle to make myself go out even though i know once i am outside i feel much better in myself.
I find having things to do from waking up to going to bed helps greatly, i plan my days with no rest periods (unless i need a duvet day in which i just accept i will do nothing but sleep, watch tv and talk on here) and always try to go out even if it is just to window shop in the local town.
I think why i feel this way is down to isolation, i know no one will check on me, no one would be concerned about me if they hadn't seen me for a week or two (i have no carer at present) so the 'whats the point' bug hits.
finding things you enjoy doing and things which take your mind away from the depressive thoughts helps. reading others difficulties on here, doing a soduko, playing with my gerbils all help me feel better and get my head in a place where i feel up to going out.I also make sure the house is not quiet, i always have the tv or my favourite music playing, not to listen to, but as background noise to break the silence and ground me.
everyone need caring for and those of us who are totally alone in the world often miss this, i too would love to be in hospital being cared for, but know this is not the answer, i need to learn to care for myself because only myself will never let me down.

trying to kill yourself will not work unless it is really your time and you are not in control of that. trust me i know by much experience!

hope this helps, you are not alone x