I really dont know how to put this but iam rather new to bass played for like 3months whith no bass teacher(mainley cause there are non where i live)
And at times i just lose my motivation to play.

I might be sitting around thinking of playing my bass then i get this though in my head ''Nah man i dont feel like it,but on the other hand i want to play but i just dont feel it in my body'' And if i force myself and try i feel like iam just out of rythm and completley lost and cant learn whatever iam doing.

This Usaly happens when iam tired ore had a badday and such and when i feel totaly lost at what iam doing.
Moral goes from Happy to ''ah the heck whith it''
But this dosent happen that often but how do i keep my good spirit up i want to play for sure but at times i just feel the ''Ah Nevermind this''

Hope i didnt bore you

see I used to be the opposite of you

playing when Id had a crap day was my way of releasing the stress

but these days when Im stressed I play ****, but these days I play mellower music, maybe thats why??

anyways, dont force it, or you'll lose all enjoyment for the instrument, just play when you want to, dont worry about how often it is, or if you dont feel like you're improving

if you're like me (who's also self taught) you'll go months thinking you're getting no better then suddenly come on in leaps and bounds, then months of no improvement again...it's just a time thing, the skills slowly build up,then suddenly slot into place

Quote by the humanity
I'm just joking Moog. you know nothing can tear our friendship apart, not even the fact we are miles apart, I am right there beside you, yelling, "Chug it, ya little wimp!"
Iam guitarist and not a bass player but i think in this case it doesn´t matter.
You should ask yourself:

Why I want to learn bass guitar?

Do I want to play in a band?
Do I want to create my own music?
Do I want to get professionel and perform with virtuosity?
Do I want to play like my idols?
Which kind of music I want to play?
3-Chord catchy bubblegum pop^^, jazz or do I want to play in a Death Metal band?

Of course you can ask yourself more questions.
So set your goals write them down on a paper and this paper should be always in front of you and create a practise plan what do you want to do.
For example(electric guitar)

Sweep Picking 15min
Alternate Picking 15 min
Working on a song 15min

and also have the practise plan everytime in front of you.
And also remember it´s better you are doing every day a half hour instead of sitting at sunday and practise once in a week 14 hours.
I know that is hard to stay motivated at the first months, but if you really want you have to do it.
How skippy_moogoose said. It can be that you are practising, practising and practising with no effort, but at someday it will make "click" and you will get better.
On other motivation is maybe to get a friend who also playing bass guitar or another instrument, that you can jam with him.

Hope I´ve helped you

Greets 40BPM
I don't know about anybody else but I can't play bass angry. I feel it's a happy instrument and expresses my feelings when I play. And I don't really like metal bass I like funk bass. I have to be in a good mood to play funk bass. When im in a bad mood but still want to play music, I usually go up to my friends house and chug out some angry power chords. :]
Ibanez SR400QM
Squier P-Bass
Fender Rumble 100 2x10
Concertmate-990 Keyboard
BBE Stomp Sonic Maximizer
Squier Stratocaster
Fender 15w Guitar Amp
I'm in the same position as you, been playing since January.

Sometime I feel hopelessly bad at bass and wanna stop for a while. If you don't feel up for it, leave it, play when you want.

I have John Entwistle biography recorded on my Sky box, so thats inspiring.