In DnD 5e, when a character is affected by the spell Sleep, they are:
'unconscious until [either] the spell ends, the sleeper takes damage, or someone uses an action to shake or slap the sleeper awake.' (SRD p.180)
For parallel stipulations, see also the spells Eyebite and Symbol, and the draconic Sleep Breath ability.
And, an unconscious person:
'can’t move or speak, and is unaware of its surroundings'(SRD p.359)
So in summary, the only ways to wake up a creature afflicted by magical sleep (with the exception of the high level spell 'Prison') are:
- to end the spell affecting them;
- to do damage to them; or
- for another character to use their action to physically wake them.
Things like loud noises, or flashing lights, which might normally be considered to wake a person, in real life, are (RAW) ineffective because they are considered to be 'unaware of their surroundings'.
RAW, does it require the same level of intervention to wake someone from a mundane sleep, as from a magical one?
Obviously, mundane sleepers are not under the affect of a spell, so can't be woken by the spell ending. But, is anything else different?
Are characters that are mundanely asleep considered to be Unconscious in the same way as characters that are magically asleep (i.e. immune to the impact of light and noise)?
Are there any ways to wake someone from a mundane sleep other than doing damage to them or using an action?
In my own research, I have found that the Wizard and Ranger spell Alarm is able to wake its sleeping caster (SRD p.114). However, this an example of the sleeper waking themselves, rather than being woken by something external. It also has a very niche application to the broader question of 'how can I wake mundanely sleeping people?'.
In this question I am interested only in waking people prematurely from their sleep (ie. being disturbed during their sleep).
An in-game reason for waking characters would be the sentry trying to alert the PCs to a night-time ambush upon their camp. In the past I have treated sleeping PCs as 'surprised' in the first round of combat but woken by the sentry's shouting, and able to act in the second round. I now wonder if this was not the correct way to manage the situation.
All this is laid out in Xanathar's Guide to Everything on page 77 in the section describing the optional rules for sleeping creatures.
Yes, sleeping creatures are unconscious regardless of the nature of their sleep:
However, if that creature is sleeping naturally it is not immune to sounds at least:
XGtE also lays out the specific rules for waking a naturally sleeping person with sounds:
Nothing is said about waking up a sleeping person with light so this would have to be a DM call.
See this question for more discussion on the effects of sleeping on perception: Perception While Sleeping.