How do I get nausea and hunger potions?

How do I get the hunger and nausea potions that are unavailable in the creative mode inventory?

I've seen Youtubers doing it but I cannot get them with commands that I have tried.

Is a mod needed to get them? If not how can I get them?

Mods are not needed to do this. You can get all these potions and more with commands.

For a swiftness potion:

/give <player> minecraft:potion 1 0 {Potion:"minecraft:swiftness"} 

For a hunger potion:

/give <player> minecraft:potion 1 0 {Potion:"minecraft:hunger"} 

For a nausea potion:

/give <player> minecraft:potion 1 0 {Potion:"minecraft:nausea"}

If you want the effect to be amplified (e.g. Strength 4 or Speed 18 etc), you could use this:

/give @p potion 1 0 {CustomPotionEffects:[{Id:(id of the potion),Duration:(number of ticks it should last),Amplifier:(amplifier value)}]}

If you want more than one effect, this also works:

/give @p potion 1 0 {CustomPotionEffects:[{Id:#,Duration:#of ticks,Amplifier:#},{Id:#,Duration:#of ticks,Amplifier:#},{Id:#,Duration:#of ticks,Amplifier:#},{...}]}

If the amplifier is negative, it will do the opposite effect. For example, an amplifier value of -2 on a health potion will reduce your maximum health. On a Strength potion, it will reduce the amount of damage you deal.

You can just do this command to get nausea potion, and just do the same for hunger but change the 9 to 15.

/give @a potion 1 8256 {CustomPotionEffects:[{Id:9,Amplifier:10,Duration:600}]}

If you want to get a nausea potion, use this command:

/give {Player} minecraft:potion 1 0 {CustomPotionEffects:[{Id:9,Duration:100}]}

As you can see my Duration is set to 100 is because by default, it will not last long, so just change the Duration into a higher number to make it last longer.

In 1.13/1.14, it is the following:

/give @p minecraft:potion{CustomPotionEffects:[{Id:9b,Amplifier:1b,Duration:1200}]} 1