Why does the same temperature feel hotter at night? For example, 70 degrees literally feels hot at night when outside but during the day 70 degrees feels just mild when outside. Why is that? And another example is that it feels hotter at night in your house during the summer than during the day and why is that when it is hotter outside during the day and cooler at night but the opposite when inside your house?
Could the answer be that the temperature falls at night compared to what it was during the day? It is unlikely to stay the same temperature during the day and night on a regular basis. The drop of temperature would increase the relative humidity, compared to the day, and so it will feel 'muggier' at night, which might lead to you thinking it feels hotter. The vague idea I'm proposing is that the 'heat index' increases at night or at least stays similar. Your brain may then expect it to feel cooler at night and so notice the heat more.
For example if it's 90°F and 55% humidity then the heat index is 97°F. If at night these readings change to 84°F and 90% humidity the heat index would be 98°F. Combined with the psychological effect of expecting it to be cooler at night may account for your experience? (I just plucked those numbers to give an example of the effect I am mention. The change of relative humidity for a 6°F temperature change is probably wrong.)
A physical explanation makes no sense at all as we know the temperature continues to fall. In addition, all the surfaces that emit IR at night also do during the day, as IR radiation is just a function of temperature.
The answer has to be local environmental, biological or psychological.
Local environmental - humidity can rise at night, and air currents fall reducing evaporation and thus raising perceived temperature.
Biological - In a poorly ventilated room, humidity can rise at night and body warmth can also raise the temperature.
Psychological - Your sensitivity to heat may be higher.
During the day, the sunlight is kept out of your house by the roof (assuming you don't have a glass ceiling or windows on your roof). At night, the sun sets and the outside atmosphere is allowed to emit infrared radiation. If there are clouds out, they emit infrared radiation back down to the surface. The atmosphere, itself, also emits radiation back (greenhouse effect), so the surface doesn't get too cold.
Now let's compare what happens at night in your house. Presumably, your roof and house absorbs a lot of radiation during the day. During the night, your house emits radiation, but more than outside, since it is hotter (Stefan-Boltzmann equation). Your roof/ceiling emits radiation both inside and outside the house. This keeps the radiation "trapped" inside the house.
Because you are actually hotter.
Body temperature changes fairly predictably though the day and varies by several degrees.
Your body temperature is highest a few hours before you go to bed (assuming a normal diurnal work schedule). It drops through the night which is why you often feel coldest in the early morning. this pops up a lot in sleep studies since people often feel like they don't need a blanket when they go to sleep and wake up in the early morning desperately wanting one.
If you are a little warm during the day you are going to be very warm later in the day crawling into a well insulated bed reflecting a lot of that heat back, but may well wake up feeling cold.
Assuming you are talking about the sensed temperature outdoors...
Solar heating of the surface creates circulations at various scales. One example is a seabreeze, which occurs due to differential heating between land and water and can occur at any scale.
So winds are generally stronger during the day. As the wind blows across your body, heat is removed from you and given to the atmosphere.
Generally stronger winds during the day leads to more heat loss from the body for a given air temperature.