Can you sit upright, even if you can't stand? Both answers are below — read the one that matches your situation.
If you can sit upright
You're able to sit upright, but can't stand for prayer.
What to know
This is directly and clearly addressed in hadith — praying sitting when you have a genuine reason isn't a lesser or incomplete prayer. It's the correct way for you to pray right now.
What you can do
Pray sitting, performing your normal recitation.
For ruku (bowing) and sujood (prostration), lean/tilt forward from your seated position — sujood should be tilted lower than ruku.
The rest of the prayer (tashahhud, tasleem) continues seated as normal.
Worth knowing: This concession is specifically for obligatory prayers when standing is genuinely difficult or harmful — not for general tiredness. If you're able to stand but simply find it hard, it's worth trying to stand for at least the parts you can manage.
The same hadith that permits sitting also explicitly extends to lying down when even sitting isn't possible — this is a complete, valid way to pray, not a partial one.
What you can do
Pray lying on your side, facing the Qibla direction if possible.
Use small head-tilts or eye movements (whatever you're capable of) to indicate the transitions between standing, bowing, and prostration.
If facing the Qibla itself isn't possible due to your condition, pray in whatever direction you're able to — the obligation is waived for what's genuinely beyond your ability.