Can you restart data service with full strength & orange indicator?
While I haven't seen that issue, you can restart the radio.

Dial *#*#INFO#*#*, choose Phone info and scroll down.  Click the Turn off radio button, then click its replacement, cunningly called Turn on radio.

A Nexus 5, being Google, should support the standard android_secret_code URIs, so INFO should be present. Other vendors may replace/remove/augment those, so bets are off on anything not directly from Google.