How to stop myself sleeping with newborn in my arms

So my son wakes at 11pm,2,4 and 6.30am

But the 4am wake is a killer for me. I’ll feed him and let him rest on me for a small time as he has acid reflux and there’s no putting him down straight after a feed. All the other wake up times I can do it where I put him back to bed but the 4am feed is where I end up falling asleep with him in my arms. I’m laid upright and on my back but I scare myself every morning when I wake and he’s still in my arms. I just can’t shake the habit now

Can anyone help?

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