[toss1]

That sounds like a good idea but the physics mean you have a far greater likelihood of painfully regretting that choice; "It seemed like a good idea at the time" will be no solace.

Using an example of a 350kt airburst on NukeMap[0], the fireball radius is 700m with an area of 1.53 km². The Thermal Radiation Radius with 3rd degree burns is 7.67 km with an area of 185 km². The Light Blast Damage Radius is 13.9 km with an area of 610 km². While the numbers will be different for different yields, the basic ratios will be the same.

This means that your person in the lawn chair is highly unlikely to get to unconscious bliss in 20ms. They are 120 times more likely to enjoy the full experience of 3rd degree burns and ~400 times more likely to get significant injury while still being alive.

It seems far better to take shelter and do all you can to survive intact, and help others. If the situation on the other side is intolerably bad, you'll likely be able to find ways to end your situation far less painfully vs being naked against a nuke blast.

[0] https://nuclearsecrecy.com/nukemap/